Forty days after Jesus rose from the dead, He ascended into Heaven. After the Ascension, almost everyone in Jerusalem was against any of Christ’s followers. Therefore, the Blessed Virgin Mary, the apostles, and perhaps other early Christians went into hiding in the upper room, the Cenacle, where Christ celebrated the Last Supper. They waited in prayer and fasting from the Ascension, waiting for the promised Holy Spirit to do something which would enable them to evangelize. On Pentecost Sunday, often called the “birthday of the Church,” the Holy Spirit descended on the Christians in the upper room, in the form of “tongues as of fire” (Acts 2:3).
The Holy Spirit enabled the apostles to miraculously speak different languages, called glossolalia. After receiving the Holy Spirit and the gift of tongues, the apostles went out to evangelize; and many people “were bewildered, because each one heard [the apostles] speaking in his own language” (Acts 2:6). However, some people through the centuries, in order to disprove Christianity, denounce the fact that the apostles had glossolalia, echoing the accusation of some of the crowds present on Pentecost: “[t]hey are filled with new wine” (Acts 2:13).
But they were clearly not drunk, for they spoke eloquently. As St. Peter tells the crowds: “these men are not drunk, as you suppose, since it is only the third hour of the day; but this is what was spoken by the prophet Joel: ‘And in the last days it shall be, God declares, that I will pour out my Spirit upon all flesh…And it shall be that whoever calls on the name of the Lord shall be saved.’” (Acts 2:16-17, 21). Indeed, St. Peter’s words convinced enough souls that “about three thousand souls” were baptized that day (Acts 2:41). Pentecost is called the birthday of the Church because the Holy Spirit began to guide her on that day, when He was poured out on the first Christians.
But Pentecost was more than just the beginning of the Catholic Church. It was the fulfillment of numerous prophecies articulated throughout the Old Testament, in which the Lord promised Israel through King David that He would not “abandon [them] to Hades, not let [them] see corruption” (Acts 2:27). But King David died and “his tomb[‘s]” existence was known in the apostles’ time” (Acts 2:29). Therefore, St. Peter declares, David “spoke of the resurrection of Christ, that he was not abandoned to Hades, nor did his flesh see corruption” (Acts 2:31). Pentecost is for all the Jewish people, as well as the New Israel (the whole world), the great extension of grace through God’s Church to mankind. St. Peter’s speech in Acts 2:22-36 also gives evidence for the authority of the Church to make definitive teachings by the power of the Holy Spirit received at Pentecost. When Peter asserts what David foretold concerning Christ, he speaks “as one who had authority,” as it was said of Christ (Mt 7:29). Of course, St. Peter is not the Christ, so how can he speak with this authority? He does so by the power Christ has given him, and by him the newborn Church, to teach authoritatively in matters of faith and morals (scriptural exegesis being a matter of faith). In a way, He becomes Christ’s mouthpiece, proclaiming to the world the Gospel message.