THE WHEN AND THE WHY TO USE THE GIFT OF LANGUAGES

Here is a little more background on Pentecost:

Pentecost is the old Greek and Latin name for the Jewish harvest festival, or Festival of Weeks (Hebrew חג השבועות Hag haShavuot or Shevuot, literally “Festival of Weeks”), which can be found in the Hebrew Bible. Shavuot is called the Festival of Weeks (Hebrew: חג השבועות, chag ha-Shavuot, Exodus 34:22, Deuteronomy 16:10 ); Festival of Reaping (Hebrew: חג הקציר, chag ha-Katsir, Exodus 23:16 ), and Day of the First Fruits (Hebrew יום הביכורים, Yom ha-Bikkurim, Numbers 28:26 ).The reading of the Book of Ruth is traditionally done in Jewish tradition at Pentecost, which links with the agricultural/harvest theme of the day.
http://en.wikipedia.org/wiki/Pentecost

PENTECOST (“fiftieth”):

Name given by the Greek-speaking Jews to the festival which occurred fifty days (ἡ πεντηκόστη, sc. ἡΜέρα = “Ḥag Ḥamishshim Yom”; comp. Lev. xxiii. 16) after the offering of the barley sheafing the Passover feast (Tobit ii. 1; II Macc. xii. 32; Josephus, “Ant.” iii. 10, § 6; I Cor. xvi. 8; Philo, “De Septenario,” §21). The Feast of the Fiftieth Day has been a many-sided one (comp. Book of Jubilees, vi. 21: “This feast is twofold and of a double nature”), and as a consequence has been called by many names. In the Old Testament it is called the “Feast of Harvest” (“Ḥag ha-Ḳaẓir”; Ex. xxiii. 16) and the “Feast of Weeks” (“Ḥag Shabu’ot”; ib. xxxiv. 22; Deut. xvi. 10; II Chron. viii. 13; Aramaic, “Ḥagga di-Shebu’aya,” Men. 65a; Greek, έορτὴ έΒδοΜάδων), also the “Day of the First-Fruits” (“Yom ha-Bikkurim”; Num. xxviii. 26; ήΜέρα τῶν νεῶν, LXX.). In the later literature it was called also the “closing festival” (“‘aẓeret”; Ḥag. ii. 4; Aramaic, “‘aẓarta”; Pes. 42b; Greek, ἄσαρθα Josephus, l.c.). It is called, too, the “closing season of the Passover” (“‘aẓeret shel Pesaḥ”; Pesiḳ. xxx. 193) to distinguish it from the seventh day of Passover and from the closing day of the Feast of Tabernacles, i.e., the end of the fruit harvest (Lev. xxiii. 36; Num. xxix. 35; Deut. xvi. 8).

Connection with Harvest.
In Palestine the grain harvest lasted seven weeks and was a season of gladness (Jer. v. 24; Deut. xvi. 9; Isa. ix. 2). It began with the harvesting of the barley (Men. 65-66) during the Passover and ended with the harvesting of the wheat at Pentecost, the wheat being the last cereal to ripen. Pentecost was thus the concluding festival of the grain harvest, just as the eighth day of Tabernacles was the concluding festival of the fruit harvest (comp. Pesiḳ. xxx. 193). According to Ex. xxxiv. 18-26 (comp. ib. xxiii. 10-17), the Feast of Weeks is the second of the three festivals to be celebrated by the altar dance of all males at the sanctuary. They are to bring to the sanctuary “the first-fruits of wheat harvest,” “the first-fruits of thy labors which thou hast sown in the field.” These are not offerings definitely prescribed for the community; “but with a tribute of a free-will offering of thine hand . . . shalt thou [the individual] rejoice before the Lord thy God, thou and thy son and thy daughter, . . . the Levite that is within thy gates, and the stranger, and the fatherless, and the widow” (Deut. xvi. 9-12). In Lev. xxiii. 15-22, however, there is a regularly appointed first-fruit offering which the whole community must bring. It consists of two first-fruit loaves (“leḥem ha-bikkurim”) of new meal, of two-tenths of an ephah, baked with leaven. The loaves were to be waved; hence the name “wave-loaves” (“leḥem tenufah”). Furthermore, various animal sacrifices were enjoined, and no work was permitted. In Num. xxviii. 26-31 the main pentecostal offering is one of new meal (“minḥah ḥadashah”). There is also a list of grain and animal offerings differing somewhat from that in Lev.xxiii.15-22. These offerings are to be made in addition to the fixed daily offering. In Men. iv. 5, x. 4 the list of Leviticus is referred to the sacrifices directly connected with the loaves, and the Numbers list is referred to the sacrifices for Pentecost considered as a special festival; the one was designated for the journeyings in the desert; the other was added after the Israelites had entered the promised land. The concluding festival of the harvest weeks was largely attended (Josephus, l.c. xvii. 10, § 2; idem, “B. J.” ii., iii. 1; Acts ii. 5).

—In Rabbinical Literature:
The festival is known in Mishnah and Talmud as “‘Aẓeret” ( or ), excepting in Megillah Ta’anit i., where (= “the Feast of Weeks”) occurs, which is explained as meaning “‘Aẓeret.” “‘Aẓeret” is usually translated a “solemn assembly,” meaning the congregation at the pilgrimage festivals. The name is applied also to Passover (Deut. xvi. 8) and to Sukkot (Lev. xxiii. 36). Ibn Ezra thinks “‘Aẓeret” denotes a holy day, a day of rest and cessation from work (comp. = “detained,” I Sam. xxi. 7). In post-Talmudic and geonic literature the Biblicalname “Shabu’ot” was resumed. Pentecost falls on the 6th of Siwan and never occurs on Tuesday, Thursday, or Saturday. Outside of Palestine the Orthodox Jews have since the exilic period celebrated the following day also, as “the second day of Shabu’ot.” Pentecost is the fiftieth day of ‘Omer, beginning from the second day of Passover. During the existence of the Temple the first-fruits were offered as well as a sacrifice of two loaves of bread from the new harvest, etc. (Lev. xxiii. 15-21).

“The Morrow After Sabbath.”
Regarding the Biblical commandment to offer the ‘omer “on the morrow after the Sabbath” = (ib. verse 11), the Rabbis maintained that “Sabbath” here means simply a day of rest and refers to Passover. The Sadducees (Boethusians) disputed this interpretation, contending that “Sabbath” meant “Saturday.” Accordingly they would transfer the count of “seven weeks” from the morrow of the first Saturday in Passover, so that Pentecost would always fall on Sunday. The Boethusians advanced the argument “because Moses, as a friend of the Israelites, wished to give them an extended holy day by annexing Pentecost to the Sabbath.” Johanan then turned to his disciples and pointed out that the Law purposely fixed the interval of fifty days in order to explain that the seven weeks, nominally, do not necessarily begin from Sunday (Men. 65a, b). See also Pharisees.

Some claim that this controversy was the reason for the substitution by the Talmudists of “‘Aẓeret” for “Shabu’ot” or “Weeks,” on which the Sadducees, and later the Karaites in the geonic period, based their adverse contention. Another reason might be to avoid confusion with “shebu’ot” = “oaths.” The Septuagint translation τῆ ἑπαύριον τῆς πρώτης (“on the morrow of the first day”) confirms the rabbinical interpretation. Onḳelos paraphrases “mi-batar yoma ṭaba” (=”from after the holy day”). The Karaites accepted the Sadducees’ view. They claim to have advanced “lion” (powerful) arguments at the time of Anan (840). In this discussion, they say, Anan sacrificed his life(“Apiryon ‘Asah Lo,” ed. Neubauer, § 6, p. 11, Leipsic, 1866). Ibn Ezra (ad loc.) argues against the contention of the Karaites and claims that as all other holy days have fixed days in the month, it would be unreasonable to suppose that Pentecost depended on a certain day of the week. The original contention of the Sadducees was one of the reasons for fixing the Christian Passover on Sunday, in the year 325 (Pineles, “Darkeh shel Torah,” p. 212, Vienna, 1861).

The Cabalists and Pentecost.
The traditional festival of Pentecost as the birthday of the Torah ( = “the time our Law was given”), when Israel became a constitutional body and “a distinguished people,” remained the sole celebration after the Exile. The Shabu’ot prayers and Maḥzor have references to this and particularly to the precepts deduced from the Pentateuch. The cabalists arranged a special “tiḳḳun” for Pentecost eve, consisting of excerpts from the beginning and end of every book of the Bible and Mishnah, which abridgment they considered tantamount to the reading of the complete works, and accepted as the approval of the Law. Apparently the custom of studying the Law all night of Pentecost is old (Zohar, Emor, 98a); but there is no record of the practise prior to the Safed cabalists headed by Isaac Luria in the sixteenth century. The custom has since been observed in the eastern states of Europe, and particularly in the Orient.

Tiḳḳun Lel Shabu’ot.
The reading occupies the pious till morning; others finish it at midnight. The collection is called “Tiḳḳun Lel Shabu’ot” (=”Preparation for Pentecost Eve”; comp. the “Tiḳḳun Lel Hosha’na Rabbah” for Tabernacles). The Pentateuch reading contains three to seven verses from the beginning and the end of every “parashah” (“sidra”). Some of the important sections are read in full, as follows: the days of Creation (Gen. i. 1-ii. 3); the Exodus and the song at the Red Sea (Ex. xiv. 1-xv. 27); the giving of the Decalogue on Mount Sinai (ib. xviii. 1-xx. 26, xxiv. 1-18, xxxiv. 27-35; Deut. v. 1-vi. 9); the historical review and part of “Shema'” (ib. x. 12-xi. 25). The same method is used with the excerpts from the Prophets: the important ch. i. of Ezekiel (the “Merkabah”) is read in full. The Minor Prophets are considered as one book: the excerpts are from Hos. i.1-3, Hab. ii. 20-iii. 19, and Mal. iii. 22-24 (A. V. iv. 4-6). Ruth is read in full; and of the Psalms, Ps. i., xix., lxviii., cxix., cl. The order of the twenty-four books of the Scriptures is different from the accepted one: probably it is an ancient order, as follows: (Torah) Five Books of Moses; (Prophets) Joshua, Judges, Samuel, Kings, Isaiah, Jeremiah, Ezekiel; (Minor Prophets) [Hagiographa] Ruth, Psalms, Job, Proverbs, Ecclesiastes, Song of Solomon, Lamentations, Daniel, Esther, Chronicles, Ezra = 24 books. Next, the excerpts from mishnayyot are read, the beginning and end of every treatise, in all sixty-three, with some important chapters in extenso; next, the “Sefer Yeẓirah”; the 613 precepts as enumerated by Maimonides (see Commandments, The 613). Later, excerpts from the Zohar bearing on the subject were added, with opening and concluding prayers. The whole reading is divided into thirteen parts, after each of which a “Ḳaddish di-Rabbanan” is recited.

The Zohar calls the time between Passover and Pentecost the “courting days of the bridegroom Israel with the bride Torah.” Those who participate in the tiḳḳun celebration are the Temple-men = ” of the King [God].” The Zohar has two epigrams on Pentecost: (1) “In the twin month [zodiac sign of Gemini] the twin Law [written and oral] was given to the children of twin Israel [Jacob and Esau].” (2) “In the third month [Siwan] the treble Law [Pentateuch, Prophets, and Hagiographa] was given to the third [best] people” (Zohar, Yitro, 78b).

Because the Law was given on Pentecost, the Rabbis wished to make that day the most enjoyable holy day. R. Joseph ordered a third (best) calf for the festival, saying: “Were it not for this day how many Josephs would there be in the street!” (“without the Law there would be no distinction of scholarship,” Pes. 68b). A popular custom on Pentecost is to eat dairy foods and cheese-cakes in honor of the Law, which is likened to “honey and milk” (Cant.iv. 11). The meat meal follows the milk meal. These two meals represent the two loaves of bread, formerly offered in the “bikkurim” offering at the Temple service.

In the synagogue the scroll of Ruth is read because the story of Ruth embracing Judaism and the description of the scene of harvesting are appropriate to the festival of the Law and of the harvest. Another reason given is that King David, a descendant of Ruth, died on Pentecost (“Sha’are Teshubah” to Oraḥ Ḥayyim, 494).

Floral Decorations and Confirmation.
The custom widely prevails of displaying greens on the floors and of otherwise decorating the home and the synagogue with plants, flowers, and even with trees. The greens serve to remind one of the green mountain of Sinai; the trees, of the judgment day for fruit-trees on Pentecost (R. H. i. 2); they also commemorate the harvest festival of former times.

The rite of confirmation for Jewish girls in the synagogue on Pentecost was introduced by the Reform party. This festival was selected because it was the birthday of Judaism. The story of Ruth’s recognition of the Jewish religion gives color to the exercise (see Confirmation).

The exact day on which the Law was given is, however, in dispute. The Rabbis say it was the 6th of Siwan; according to R. Jose it was the 7th of that month. All agree that the Israelites arrived at the wilderness of Sinai on the new moon (Ex. xix. 1), and that the Decalogue was given on the following Saturday. But the question whether the new-moon day fell on Sunday or Monday is undecided (Shab. 86b).

The three days preceding Pentecost are called “the three days of the bounds” () to commemorate the incident of the three days’ preparation before Mount Sinai (Ex. xix. 11, 12). These days are distinguished by the permission of marriage celebrations, which are prohibited on the other days of Sefirah save Lag be-‘Omer and Rosh-Ḥodesh. See Aḳdamut; First-Fruits; Flowers in the Home and the Synagogue; Law, Reading from the; Pilgrimages to the Holy Land; Prayer.

Bibliography:
Halakot Gedolot, ed. Berlin, 1888, i. 146;
Shulḥan ‘Aruk, Oraḥ Hayyim, 494;
Der Jude, pp. 42-48. Leipsic, 1769;
Hebrew Review, ii. 152-157;
Addresses to Young Children, xxi. 189-201, London, 1858;
Friedländer, Jewish Religion, pp. 393-394, 2d ed., London, 1900;
Steinschneider, Hebr. Bibl. xiv. 64. For the interpretation of “the morrow after Sabbath”: Aaron of Nicomedia (Karaite), Keter Torah, Lev. 65a, Eupatoria, 1866;
Pinsker, Liḳḳuṭe Ḳadmoniyyot, Appendix, p. 96;Cusari, iii. 41;
Lichtenstadt, Ḳunṭros mi-Moḥorot ha-Shabbat, Vienna, 1860;
Gottlober, Biḳḳorotle-Toledot ha-Ḳara’im, p. 84, Wilna, 1865;
Ha-Maggid, 1840, iv., No. 40; 1879, xxiii., No. 22;
Frankel, Vorstudien zu der Septuaginta, pp. 190-191, Leipsic, 1841;
Geiger, Urschrift, p. 138, Breslau, 1857;
Wellhausen, Pharisäer und Sadducäer, p. 59, Bamberg, 1874.
According to the Sects.
—Critical View:

In the Old Testament the exact day of the celebration of Pentecost is not given. It is seen from Ex. xxiii. 10-17, xxxiv. 18 that it was celebrated some time in the late spring or the early summer. In Deut. xvi. 9 (R. V.) the date is given “seven weeks from the time thou beginnest to put the sickle to the standing corn.” In Lev. xxiii. 15, 16 the date is more definitely given: “And ye shall count unto you from the morrow after the Sabbath, from the day that ye brought the sheaf of the wave-offering; seven Sabbaths shall be complete. Even unto the morrow after the seventh Sabbath shall ye number fifty days.” The meaning of the word “Sabbath” in the phrase “after the Sabbath” (“mimoḥorat ha-Shabbat”) and, consequently, the question as to the day upon which the Pentecost was to fall have constituted a chief point of difference between Jewish sects (comp. Charles, “The Book of Jubilees,” vi. 22, 32; xvi. 3). Sabbath may mean either a “festival” (Lev. xxv. 2, 46) or the weekly Sabbath. In the general sense of “festival” the day of bringing the sheaf of the wave-offering (“yom ḥanef”), i.e., “the day after the Sabbath,” would mean the day after either the first or the last day of Passover. (a) That the “Sabbath” in this case means the first day of Passover is the view of the Septuagint, Targ. pseudo-Jonathan, Targ. Onḳelos, Josephus (“Ant.” iii. 10, § 5), Philo (“De Septenario,” § 20; comp. Ḥag. ii. 4, Men. vi. 1-3), and of the later rabbinic literature. Since, according to this view, the sheaf-offering was waved on the 16th of Nisan, Pentecost, fifty days later, was celebrated on the 6th of Siwan without regard to the day of the week on which that fell. (b) That the “Sabbath,” according to the general meaning “festival,” signifies the seventh day of Passover, i.e., 21st of Nisan, without regard to the day of the week, is the view of the Falashas of Abyssinia, the Syriac version of Lev. xxiii. 11, 15, and the Book of Jubilees (c. 135 B.C.). The “day after the Sabbath” is, accordingly, the 22d of Nisan. The Falashas reckon fifty days according to a system of months alternating thirty and twenty-nine days, the Feast of Weeks thus falling on Siwan 12. In Jubilees the Feast of Weeks and Feast of First-Fruits of the Harvest are celebrated on Siwan 15 (Jubilees, xvi. 1, xliv. 4). Reckoning fifty days backward, with an ecclesiastical month of twenty-eight days, one arrives at Nisan 22 as the date when the wave-sheaf was offered. (c) The term “Sabbath,” as is shown above, was taken to mean also the weekly Sabbath.

Association with the Giving of the Law.
It is difficult to determine whether the controversy as to the date of the celebration of Pentecost was merely a question of calendation or whether it had its origin in the attempt to assign to the festival a historical motive such as was lacking in the Old Testament. Just as Passover and Tabernacles were associated with historical events, so Pentecost was brought together with the day on which the Torah was given on Sinai (Ex. R. xxxi.; Shab. 88a; Pes. 68b; Maimonides, “Moreh,” iii. 41; comp. Ex. xix. 1). That this association had something to do with the calendar controversy would seem to follow from the fact that both Philo and Josephus make no mention of either the giving of the Law on that day or of the calendar dispute. Some insight into the origin of this association of Pentecost with the giving of the Law is afforded by Jubilees where the covenant with Noah as regards the eating of blood is made on the Feast of Weeks. This covenant is renewed with Abraham and with Moses on the same day. Itneeded but a step for later times to place the covenant on Sinai also on the same day.

According to Jubilees, Isaac was born (xvi. 13), Abraham died (xxii. 1), Judah was born (xxviii. 15), and Jacob and Laban bound themselves by mutual vows (xxix. 7) on the Feast of Weeks. See Jew. Encyc. v. 374b, s.v. Festivals (Shabu’ot). The relation of the Jewish to the Christian Pentecost with its pouring out of the spirit as an analogy to the giving the Law in seventy languages is obvious.

http://www.jewishencyclopedia.com/articles/12012-pentecost

Bibliography:
Charles, The Book of Jubilees, London, 1902;
Frankel, Einfluss der Palästinensischen Exegese auf die Alexandrinische Hermeneutik, pp. 136-137, Leipsic, 1851.