"When the Day of Pentecost had fully come, they were all with one accord in one place. And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the house where they were sitting. Then there appeared to them divided tongues as of fire, and one sat upon each of them. And they were all filled with the Holy Spirit and began to speak with other tongues as the Spirit gave them utterance" (Acts 2:1-4).
The apostles, as they had been instructed, were still gathered in Jerusalem ten days after Christ ascended into heaven. It is unlikely that they were gathered in a private residence at this time but likely in one of the many spacious rooms that surrounded the temple court. This would have provided enough room for the large number of people that were about to assemble (cf. Luke 24:53). Pentecost means fiftieth, which is appropriate since the feast always landed on a Sunday, the fiftieth day after the Passover Sabbath (cf. Lev. 23:15,16). Pentecost was one of three annual feasts that every adult Jewish male was required to attend in Jerusalem (cf. Deut. 16:16). Pentecost was also known as the Feast of Harvest (first-fruits). It celebrated the gathering of the grain harvest. It is not a trivial matter to note that the first "gathering" of the gospel harvest occurred on this day. Jesus had been condemned and slain at the prior feast (Passover), and now He would be vindicated, declared as the exalted Lord and Christ, and His church would be established at this major feast. To say that the day had "fully come" simply means it was daylight. The Jewish method of reckoning time had the day technically beginning at sunset the prior evening, but such was not a suitable time to accomplish what God had in store at this time.
Although there were 120 disciples gathered back in Acts 1:15, the context here and pronoun usage indicates that it was the twelve apostles who were under consideration in Acts 2:1-4 (cf. the word "they" used in this section refers back to the "apostles" in 1:26; remember that chapter and verse divisions are added by men, not God). Additionally, it becomes clear later that it was only the apostles who received miraculous powers on this day as a result of the outpouring of the Spirit (cf. 2:7; 5:12,13).
A mighty sound that was like wind filled the place where the apostles were gathered. It was from heaven and was loud enough to gather quite a crowd, as we will see shortly. A mighty sight consisting of tongues that were like fire appeared to the apostles and "sat upon each of them" (Acts 2:3). Thus, the apostles were "all filled with the Holy Spirit" as Jesus had promised (2:4). They were completely overwhelmed by the Spirit, just as a body, when baptized in water, is overwhelmed (submerged). The result was that they received miraculous power (mental endowments, specifically) that had been promised (cf. 1:8). They were now able to "speak with other tongues as the Spirit gave them utterance." In other words, they were able to speak in other languages as the Holy Spirit empowered them to do so. The reference to "tongues" here does not mean ecstatic utterances consisting of unintelligible sounds as will be proven when we consider 2:6,8,11.
As noted from our study of Acts 1, this significant event--the outpouring of the Spirit--would signal the establishment of Christ's kingdom (cf. Acts 1:8; Mark 9:1). It would enable the apostles to accurately speak the mighty works of God. The baptism with the Holy Spirit is not a blessing for today. Even before the close of the first century, there was only "one baptism" (Eph. 4:5). Great Commission baptism, administered by men (i.e., water baptism), was to continue to the end of the age per Matthew 28:19,20.