Pentecost is simply another name for the Old Testament holy day known as "the Feast of Weeks." The Feast of Weeks, one of three annual feasts appointed in the law of Moses for Israel to observe in the Land, was a holy convocation of the whole people in Jerusalem each spring for a celebration of the harvest (Lev. 23:15-22; Dt. 16:9-12). The term "Pentecost" refers to the fact that this was the fiftieth day after the wave offering of a sheaf of grain, signifying the first fruits of the springtime harvest. The offering of first fruits was made when Israel first put the sickle to the grain to begin the process of reaping, and seven weeks after was the Feast of Weeks or Pentecost.
Interestingly, the first fruits offering took place in the midst of the seven-day Feast of Unleavened Bread that began with Passover. Israel was to offer the first fruits while still partaking of the bread of affliction and haste, the bread by which she remembers her bondage in Egypt and her redemption (Dt. 16:3). On the third day, while still looking back and still partaking of the provisions of her journey out of bondage (the rations of a nomadic life on the road), she begins looking forward in anticipation of new life, to reaping the blessings of the Land into which God brought her. To have been led into this Land involves immediate reaping of a bounty graciously given; there is no sowing, only a reaping that is to be done in constant mindfulness of her sojourn in Egypt and her liberation from servitude by God. Though Israel must go forth to labor in the fields, the fields are already white unto harvest. God gives the increase and provides the fruitful fields for the leavened bread of settled existence at rest. Israel reaps what she did not sow, being blessed of God and not by her own hand.
We are thus to connect this harvest festival with the great exodus-event. It celebrates the goal of the exodus - Israel's entry into the Promised Land, a land of milk and honey. A covenantally faithful Israel in Canaan, as God's chosen people, would enjoy bountiful harvests, reaping the rich blessings of God's gracious provisions of abundant life, being fed and satisfied and lacking nothing (Dt. 8:6-18). The plenteous harvests were signs of Israel's blessedness, signs of God's favor and beneficence, signs of God's covenant faithfulness in caring and providing for His people. They were a fruit of covenant life. The first fruits of the harvest, anticipating in faith and hope the fullness to follow, were consecrated holy unto God as a thanksgiving offering that celebrated this blessedness, this enjoyment of the end-result of the Passover/exodus that brought them to the Land and entry into covenant blessedness, thus fulfilling the redemption from Egypt. First fruits was a celebration of hope. The seven sevens (seven weeks) between the first fruits and Pentecost had eschatological significance, pointing to the fullness of rest and enjoyment, the Sabbath of Sabbaths or Jubilee.
Clearly, the Day of Pentecost in A. D. 30, fifty days after the Easter-event, must be understood as signifying the eschatological harvest. Israel's calling as the people of God was not an end in itself, for the purpose of blessing Israel only. Israel was a servant-nation, called to be the instrument through which God would bless the nations. The law given to Israel was to be her wisdom and righteousness before the nations (Dt. 4:6-8); Israel as the Servant of Yahweh was to be a light in the midst of the nations, attracting all peoples to come to worship the true God - the God of Israel. Israel's solemn assembly each year at Pentecost was the gathering of this people as themselves the first fruits of God's of a larger harvest-gathering, a harvesting of the fruit of a salvation that would extend to the nations and secure the obedience of the nations. After the exodus Jesus accomplished at Jerusalem (Lk. 9:31) as the antitypical Passover, a first fruits of the gospel-harvest is gathered, representing, anticipating, commencing the fullness of the eschatological harvest that is to be reaped from the uttermost parts of the earth. In this gathering of the first fruits, the Jewish diaspora is the first gathered and added to God's eschatological restored Israel, but they are gathered into the New-Covenant community as tokens of a harvest that is to include the nations in its scope as well. Restored Israel - the Pentecost assembly - is to publish the glad tidings out from Zion to the ends of the earth, heralding the established reign of God.
Jewish tradition associated Pentecost with the giving of the law at Sinai. Pentecost in Judaism was therefore the day of the assembly, the feast signifying the day of holy convocation when God established His covenant and constituted Israel as the holy priest-nation. Luke's account in Acts clearly has this in mind and thus expects us to understand the ekklesia in terms of Sinai-typology, the antitype-fulfillment of the Sinai-event. In the last days the nations would come to Mt. Zion; the law would issue forth out of Zion (Is. 2:2-4). This Zion-torah and Zion-assembly was the fulfillment of Israel's mission as the people of God, issuing in the blessing of the nations and a worldwide harvest. The theological significance of the Day of Pentecost in Acts is that this gathering in of the eschatological harvest of the nations has begun. The one who baptizes with the Spirit has gathered the wheat into His granary (Mt. 3:11-12).
In Acts the outpouring of the Spirit is to be understood as the eschatological-antitypical giving of the law in a New Covenant act of God - the giving of the Zion-torah to New Covenant Israel. Because of the sins of covenant-breaking Israel polluting the Land, only when the Spirit would be poured out from on high as latter-day rain from heaven would the Land yield its fruit of covenantal blessing (Is. 32:13-18, 45:8; Joel 2:18-29; 3:18), bestowing the sure mercies of David (Is. 55) that would raise up the fallen tabernacle of David (Am. 9:11-15) and so exalt Zion (Is. 2:2-4). The Spirit put into the hearts of the people is a New-Covenantal blessing, the circumcision of the hearts of the people by God and the writing of His law upon their hearts (Ez. 11:19-20; 36:26-27; Dt. 30:6; Jer. 31:31-34; 33:37-42).
We are a Pentecostal people. To be invested with the Spirit of God is to be transformed into an obedient people. The righteous requirements of the law are to be fulfilled in us by the Spirit (Rom. 8:4), making us doers of the law and not (as was Old-Covenant Israel) hearers only. Moreover, Pentecost is power from on high that equips us to be effective witnesses. We are empowered by the Spirit to successful mission, enabled to reap the fullness of the harvest, and we are sent forth to bring in the sheaves. The season of Pentecost is a time of growth and maturation, a time in which we should recommit ourselves to what it means for us to be a Spirit-people, a time to pursue sanctification (and thus theonomic life) and to engage in kingdom mission - the discipling of the nations.