In his first letter to the Corinthians, Paul tells the congregation there, “Now I will come to you when I pass through Macedonia (for I am passing through Macedonia). And it may be that I will remain, or even spend the winter with you, that you may send me on my journey, wherever I go. For I do not wish to see you now on the way but I hope to stay a while with you, if the Lord permits. But I will tarry in Ephesus until Pentecost” (1 Cor. 16:5-8). Paul probably wrote the letter from Ephesus in about AD 55, where he was based on his Third Missionary Journey, but he had to curtail his stay in that city in AD 57 because a riot broke out there opposed to the success his Gospel preaching and teaching had made. In leaving Ephesus, Paul did make a circuit around the Aegean, checking in on churches he planted in Macedonia and Greece before heading toward Jerusalem. In this circuit he made several stops on the coast of Asia Minor, but as Luke records in Acts, “Paul had decided to sail past Ephesus, so that he would not have to spend time in Asia; for he was hurrying to be at Jerusalem, if possible, on the Day of Pentecost” (Acts 20:16). Paul’s haste to be in Jerusalem in time for Pentecost raises the obvious question as to why was this holy day so important to him and what would it have meant for him to observe it?
The Old Covenant Antecedent to Pentecost: The Feast of Weeks
The name “Pentecost” comes from the Greek rendering of Leviticus 23:16 referring to the fact that it occurs 50 days after Passover. The Old Testament calls this festival day the “Feast of Weeks” (or alternatively, the “Feast of Harvest” or the “Feast of Firstfruits”), and it is described in Exodus 23:14-19, 34:22-28; Leviticus 23:15-21; Numbers 28:26-31; and Deuteronomy 16:9-12.
The 50 days referred to are counted from the day after the Sabbath during the Feast of Unleavened Bread, the broader celebration of the Passover, where a sheaf of grain was waved as a wave offering, an offering of particular dedication to the LORD (Exod. 23:9-14, Lev. 23:9-14). This period also approximates the time it took Israel to go from Egypt to Sinai in the Exodus. In Exodus 19:1, Moses notes that it was “In the third month after the children of Israel had gone out of the land of Egypt, on the same day [as the Exodus], they came to the Wilderness of Sinai.” Israel left Egypt in the middle of the month of Nisan, so including that month, Israel would have gone into its third month when it arrived at the foot of Sinai. This passage is just before God’s giving of the Law in Exodus 20. The agricultural and covenantal aspects of the Feast of Weeks laid the basis for the redemptive historical significance of Pentecost.
Agriculturally, the sheaf that would have been waved (or more likely, simply lifted up) during the Feast of Unleavened Bread probably would have been a barley sheaf, as the barley harvest would typically have been in the March-April timeframe and the offering would have been a firstfruits dedication to the LORD. The more significant cereal crop, though, was wheat, and the wheat harvest would only be just beginning in the April-May timeframe. Thus, the Feast of Weeks was at a minimum the firstfruits of the greater blessing.
The Feast of Weeks was more than just a harvest festival. Deuteronomy 16:12 grounded the Feast in the remembrance of Israel’s deliverance from slavery. It was one of the three high holy days on which all Israelite males were to appear before the LORD (Exod. 23:17), and the LORD promised to “cast out the nations before you and enlarge your borders; neither will any man covet your land when you go up to appear before the Lord your God three times in the year” (Exod. 34:24). All these things gave the Feast a covenantal significance. Appearance before the LORD, therefore, would be tantamount to vassals coming before the suzerain king to pay homage and tribute (i.e., thanksgiving and honor). It would inculcate in the Israelites a proper fear of the LORD if consistently obeyed with the right attitude, and it would bind the nation together; the shared experience and the contacts with others would get them beyond their tribal horizons.
The Leviticus and Numbers passages mentioned above contain details on the rituals that are to be done on the Feast of Weeks: there are a burnt offering, a grain and drink offerings, a sin offering, a peace offering, and a wave offering. Thus, included here were offerings for atonement, tribute, sanctification, and thanksgiving—almost the entire spectrum of offerings under the Levitical sacrificial system. The scale of the offerings is larger than normal. The sacrifices were freewill offerings offered in the spirit of thanksgiving in response to the great things God had done. In sum, God in His covenant brings His people out, and gives them the first fruits of blessing, makes them into a nation, binds them together, blesses them, and calls them to image His name among the nations in thanksgiving.
How the Feast Was Transformed Under the New Covenant
After the Mosaic period, the Feast of Weeks is not mentioned in the rest of the Old Testament. After the Exile, the Jews began rediscovering the Law, since their neglect of it earlier had resulted in the trauma of the Babylonian Captivity. The Feast of Weeks was part of this rediscovery. During the period between the Old and New Testaments, the pseudepigraphic Book of Jubilees stipulated (6:17) that the Feast was to be celebrated yearly as a covenant renewal. In addition, certain exegetical interpretations emerged that highlighted God’s gift of the Law (Torah) at Sinai. These were probably extant in the time of the New Testament and formed the background for how the Apostles understood the outpouring of the Holy Spirit at Pentecost described in Acts 2.
The major passage in the New Testament is, of course, Peter’s sermon on the Day of Pentecost in Acts 2:14-34. On that day, the Holy Spirit came upon the people assembled in the Temple and everyone begins speaking in tongues, hearing their own languages despite their ethnic differences. In Acts 2:3, the outpouring of the Holy Spirit is described as “divided tongues, as of fire,” phraseology evocative of Psalm 29:7 (“the voice of the LORD divides the flames of fire”) and of Exodus 19:16, where the word typically rendered in English “thunderings” literally means “sounds” or “voices” in Hebrew. Because of these connections, the early Christian Church often included Exodus 19 in Scripture readings for Pentecost.
When bystanders at Pentecost asked how it could be that people were understanding things in so many different languages and what explained the tumult, Peter then launched into his explanatory sermon. To understand Peter’s explanation, we have to look first at two passages, Joel 2:28-32, which Peter preached in his sermon, and Jeremiah 31:31-34, which prophesied the changes that would come about as a result of the New Covenant.
Joel’s prophecy highlights the outpouring of the Holy Spirit on God’s people, that they would be supernaturally empowered to speak God’s words for the salvation of many. It also anticipated a day of judgment, a Day of the LORD. It probably was one of the first written prophecies, and with Pentecost, it was partially fulfilled: the Spirit has come, but the Day of the LORD is still pending.
Although not cited by Peter in his Pentecost sermon, Jeremiah 31:31-34 builds on the foundation set by Joel and is the foundational passage in the Old Testament for understanding the New Covenant.
Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah—not according to the covenant that I made with their fathers in the day that I took them by the hand to lead them out of the land of Egypt, My covenant which they broke, though I was a husband to them, says the Lord. But this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people. No more shall every man teach his neighbor, and every man his brother, saying, ‘Know the Lord,’ for they all shall know Me, from the least of them to the greatest of them, says the Lord. For I will forgive their iniquity, and their sin I will remember no more.
The key part of this covenant is that the Lord says that He will, “put My law in their minds and write it on their hearts” (Jer. 31:33). The question this raises is how would the Lord do this? Paul in effect answers that question in his first letter to the Corinthians when he says, “But God has revealed them to us through His Spirit. For the Spirit searches all things, yes, the deep things of God. For what man knows the things of a man except the spirit of the man which is in him? Even so, no one knows the things of God except the Spirit of God. Now we have received, not the spirit of the world, but the Spirit who is from God, that we might know the things that have been freely given us by God” (1 Cor. 2:10-12). At Pentecost, God did not remove His law or change it, but gave His people His Holy Spirit to unite them to Himself so that they could know and obey His law. Just as the Old Covenant was inaugurated with the Feast of Weeks, so the New Covenant is inaugurated with Pentecost.
The Significance of Pentecost Today
In pulling together all these threads, what would Pentecost have meant to Paul? Paul was not simply being an observant Jew by wanting to be in Jerusalem in time for Pentecost. In Paul’s conversion account in Acts 9:1-19, there were three major touchstones which marked his preaching and teaching for the rest of his life: (1) the resurrection of Christ; (2) the union of Christ with His people; and (3) the indwelling of the Holy Spirit. It was the power of the resurrected Christ that confronted Paul on the road to Damascus. Christ’s union with His people can be seen in 9:4-5 where He twice confronts Paul about Paul’s persecution of Him. From Paul’s perspective, he was persecuting Jesus’s followers, assuming Jesus to be dead, yet Jesus so identified with His people that for them to be persecuted meant He was being persecuted. And, after the encounter with Jesus, the Holy Spirit came upon Paul when Ananias laid hands upon him. In light of this, Pentecost would have been central for Paul: the coming of the Holy Spirit occurred because the risen Christ ascended to the Father; the Spirit was the One by whom God’s people are united to Christ; and the indwelling of the Spirit transformed His attitude to the Law which he had been so zealous for, from living by the works of the Law to living by the grace of the Spirit. No wonder then that Paul was so eager to return to Jerusalem in time for Pentecost. His journey to Jerusalem to observe Pentecost is the inverse of his journey to Damascus that effected his conversion years earlier. Then, he had a mandate to crush the Christian faith before it could reach the nations, but in returning to Jerusalem for Pentecost, he was going to further the spread of the Gospel to the nations.
For us today, Pentecost tends to be under appreciated. It is a celebration of the new age ushered in by Christ, the radical change that had been wrought in redemptive history. Writing in about AD 200—in the earliest post-apostolic reference to the day—the Latin church father Tertullian of Carthage (AD 155-220) described Pentecost in his treatise, On Baptism as a most joyous time given that the resurrection of Christ had been proven to be true. One can add to Tertullian’s statement that this joyousness is also due to the coming of the Holy Spirit. So, what is the significance of the coming of the Spirit? First, we are joined to Christ through the Spirit, therefore the judgment Christ has borne is our judgment and the righteousness He possessed is our righteousness. Second, Christ promised He would never leave us. Because we are joined to Him in the Spirit, He never will. Third, we are being conformed by the Spirit into the image of Christ. This is a tie back to the Law, but also an advancement on it, as we, through the Spirit’s work, increasingly reflect the holy character of Christ that the Law foreshadowed. Lastly, just as the firstfruits are brought in so to in this period between the first and second coming of the Lord, the nations are being gathered in. This ties back to the promise made to Abraham, and reverses the curse imposed at Babel. Where the nations were dispersed, they are now being drawn together. For these reasons, Pentecost—arguably even more than Easter—brings into perspective the full scope of God’s redemptive work.
 One such tradition surrounds the rabbinic interpretation of Ps. 68:17-18, which held that the Law which Moses received on behalf of the people was a gift from God. This interpretative tradition was fairly consistent during the intertestamental period, even though it did not fit the details of the Psalm entirely. There is a loose correlation between Ps. 68:18 and Peter’s explanation for the coming of the Holy Spirit in Acts 2:33, which Peter interpreted in a Christological manner as the gift of the Holy Spirit rather than the Law. Paul also quotes Ps. 68:18 in Eph. 4:8, similarly putting a Christological interpretation on the passage. Both probably knew of the rabbinic interpretation, and their Christological interpretations better harmonize with the text of Psalm 68:18. Thus, by correcting the rabbinic interpretation, they also are indirectly linking the Pentecost event with the giving of the Law at Sinai. See F. S. Thielman, “Ephesians” in Commentary on the New Testament Use of the Old Testament, edited by G. K. Beale and D. A. Carson (Grand Rapids MI: Baker Academic, 2007), 819-825.
 For a fuller discussion of the connections between the Jewish Feast of Weeks and the Christian Pentecost, see Oskar Skarsaune, In the Shadow of the Temple; Jewish Influences on Early Christianity (Downer’s Grove IL: Intervarsity Press, 2002), 393-397, and Paul F. Bradshaw and Maxwell E. Johnson, The Origins of Feasts, Fasts and Seasons in Early Christianity (Collegeville MN: Liturgical Press, 2011), 69-74.