Before posting the notes on Acts 2, I decided to place our lesson on Pentecost from last year first. This provides much of the background material to understand some of the significance of what is happening in Acts 2.
As the name Pentecost indicates (pentekoste), this second of the great Jewish national festivals was observed on the 50th day, or 7 weeks, from the Paschal Feast, and therefore in the Old Testament it was called "the feast of weeks." It is but once mentioned in the historical books of the Old Testament (2Ch 8:12,13), from which reference it is plain, however, that the people of Israel, in Solomon’s day, were perfectly familiar with it: "offering according to the commandment of Moses, on the sabbaths, and on the new moons, and on the set feasts, three times in the year, even in the feast of unleavened bread, and in the feast of weeks, and in the feast of tabernacles." The requirements of the three great festivals were then well understood at this time, and their authority was founded in the Mosaic Law and unquestioned. The festival and its ritual were minutely described in this Law. Every male in Israel was on that day required to appear before the Lord at the sanctuary (Ex 34:22,23). It was the first of the two agrarian festivals of Israel and signified the completion of the barley-harvest (Le 23:15,16; De 16:9,10), which had begun at the time of the waving of the first ripe sheaf of the first-fruits (Le 23:11). Pentecost, or the Feast of Weeks, therefore fell on the 50th day after this occurrence. The wheat was then also nearly everywhere harvested (Ex 23:16; 34:22; Nu 28:26), and the general character of the festival was that of a harvest-home celebration. The day was observed as a Sabbath day, all labor was suspended, and the people appeared before Yahweh to express their gratitude (Le 23:21; Nu 28:26). The central feature of the day was the presentation of two loaves of leavened, salted bread unto the Lord (Le 23:17,20; Ex 34:22; Nu 28:26; De 16:10).* The size of each loaf was fixed by law. It must contain the tenth of an ephah, about three quarts and a half, of the finest wheat flour of the new harvest (Le 23:17). Later Jewish writers are very minute in their description of the preparation of these two loaves (Josephus, Ant, III, x, 6). According to the Mishna (Menachoth, xi.4), the length of the loaf was 7 handbreadths, its width 4, its depth 7 fingers. Le 23:18 describes the additional sacrifices required on this occasion. It was a festival of good cheer, a day of joy. Free-will offerings were to be made to the Lord (De 16:10), and it was to be marked by a liberal spirit toward the Levite, the stranger, and orphans and widows (De 16:11,14). Perhaps the command against gleaning harvest-fields has a bearing on this custom (Le 23:22).
Also, in the Old Testament Pentecost was the feast which occurred fifty days after Passover. As the passover feast celebrated the exodus of the Israelites from the slavery of Egypt, Pentecost celebrates the giving of the law to Moses and thus the creation of Israel.
In the new covenant of the Messiah, the passover event takes on its new meaning as the celebration of Christ's death and resurrection, the "exodus" of men from this sinful world to the Kingdom of God. And in the New Testament as well, the pentecostal feast is fulfilled and made new by the coming of the "new law," the descent of the Holy Spirit upon the disciples of Christ. It is the recreation of Israel.
On Pentecost we have the final fulfillment of the mission of Jesus Christ and the first beginning of the messianic age of the Kingdom of God mystically present in this world in the Church of the Messiah. For this reason the fiftieth day stands as the beginning of the era which is beyond the limitations of this world, fifty being that number which stands for eternal and heavenly fulfillment in Jewish and Christian mystical piety: seven times seven, plus one.
Just as the OT Jews offered the First Fruits of harvest to God, Christ fulfills this OT feast by becoming the First Fruits of the resurrection.
*In Orthodoxy, we use leavened bread for communion rather than unleavened bread. The Eastern church has always done so and there has never been a concern for using the exact type of bread as used at the Last Supper. The OCA site states: "Christ "leavens" our lives, so to speak, and the purpose of the Eucharistic celebration is not to "recreate" or "reproduce" a past event but, rather, to participate in an event that is beyond time and space and which, in fact, continues to happen each time the Eucharist is celebrated in fulfillment of Our Lord's command." I do have to wonder if the use of leavened bread at Pentecost may account for the original usage of leavened bread. Comments are welcome on this point