The story
It began with a command to wait. After His suffering Jesus presented Himself alive to them with many convincing proofs. He appeared over a span of forty days and spoke about the kingdom of God. He told them not to leave Jerusalem but to wait for the gift the Father promised: in a few days you will be baptized with the Holy Spirit (Acts 1:3–5). Then He was taken up. They walked back to the upper room and stayed there.
They did not wait passively. With one accord they all continued in prayer, along with the women and Mary the mother of Jesus, and with His brothers (Acts 1:14). Luke gives the gathering as about a hundred and twenty (1:15). During those days they replaced Judas, and Matthias was added to the eleven apostles (1:26).
Pentecost was the Feast of Weeks, fifty days after the sheaf of firstfruits, one of the three pilgrim feasts that filled Jerusalem with visitors from across the empire (Leviticus 23:15–21). When the day of Pentecost came, they were all together in one place (Acts 2:1). The city was crowded, and the disciples were praying.
Then the sound. Suddenly a sound like a mighty rushing wind came from heaven and filled the whole house where they were sitting (Acts 2:2). They saw tongues like flames of fire that separated and came to rest on each of them (2:3). Notice how carefully Luke writes: like a wind, like flames of fire. He is telling you what it resembled, because there is nothing else to compare it to. And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them (2:4).
The noise brought a crowd. God-fearing Jews from every nation under heaven were living in Jerusalem, and they came together in bewilderment, because each one heard them speaking his own language (Acts 2:5–6). Luke lists fifteen homelands: Parthians, Medes, Elamites, residents of Mesopotamia, Judea, Cappadocia, Pontus, Asia, Phrygia, Pamphylia, Egypt, the parts of Libya near Cyrene, visitors from Rome, Cretans and Arabs. All of them heard Galileans declare the wonders of God in tongues they had never learned (2:9–11).
Not everyone was moved. Some were astounded and perplexed and asked one another, what does this mean? Others mocked and said, they are drunk on new wine (Acts 2:12–13). Peter stood up with the Eleven and answered the mockery first: these men are not drunk, as you suppose, it is only the third hour of the day, nine o'clock in the morning (2:14–15).
Then he preached, and the sermon is almost entirely Scripture. No, this is what was spoken by the prophet Joel: in the last days, God says, I will pour out My Spirit on all people; your sons and daughters will prophesy, your young men will see visions, your old men will dream dreams; even on My menservants and maidservants I will pour out My Spirit in those days; and everyone who calls on the name of the Lord will be saved (Acts 2:16–21). Peter begins the quotation with in the last days, where Joel says afterward. He is not correcting the prophet. He is telling the crowd which days they are standing in.
The center of the sermon is a man, not an experience. Jesus of Nazareth was a man certified by God to you by miracles, wonders and signs, which God did among you through Him, as you yourselves know; He was delivered up by God's set plan and foreknowledge, and you, by the hands of the lawless, put Him to death by nailing Him to the cross; but God raised Him from the dead (Acts 2:22–24). He argued from Psalm 16 that David could not have been speaking of himself, since David died and was buried and his tomb is with us to this day (2:29), and from Psalm 110 that David called this one Lord. Then the conclusion: let all Israel know with certainty that God has made this Jesus, whom you crucified, both Lord and Christ (2:36).
The crowd was cut to the heart and asked, brothers, what shall we do? Peter replied: repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit (Acts 2:37–38). Those who embraced his message were baptized, and about three thousand were added to the believers that day (2:41). The word about is Luke's own. Luke does not say where three thousand people were immersed in one day. Jerusalem's many stepped ritual baths near the temple are the practical answer, and that is an inference and not the text.
Luke's last word on that morning is the least dramatic part of it and the most demanding. They devoted themselves to the apostles' teaching and to the fellowship, to the breaking of bread and to prayer. A sense of awe came over everyone, and the apostles performed many wonders and signs. All the believers were together and had everything in common, selling their possessions and goods and sharing with anyone in need. With one accord they met daily in the temple courts and broke bread from house to house, sharing their meals with gladness and sincerity of heart and praising God. The Lord added to their number daily those who were being saved (Acts 2:42–47). The year was either AD 30 or AD 33, depending on where the crucifixion is dated; the church has counted from that morning either way.