As recorded in the beginning of the
Acts of the Apostles:
"In the first book [the Gospel of Luke], O Theophilus, I have dealt with all that Jesus began to do and teach, until the day when he was taken up, after he had given commandment through the Holy Spirit to the apostles whom he had chosen. To them he presented himself alive after his passion by many proofs, appearing to them during forty days, and speaking of the kingdom of God. And while staying with them he charged them not to depart from Jerusalem, but to wait for the promise of the Father, which, he said, "you heard from me, for John baptized with water, but before many days you shall be baptized with the Holy Spirit." So when they had come together, they asked him, "Lord, will you at this time restore the kingdom to Israel?" He said to them, "It is not for you to know times or seasons which the Father has fixed by his own authority. But you shall receive power when the Holy Spirit has come upon you; and you shall be my witnesses in Jerusalem and in all Judea and Samaria and to the end of the earth." And when he had said this, as they were looking on, he was lifted up, and a cloud took him out of their sight. And while they were gazing into heaven as he went, behold, two men stood by them in white robes, and said, "Men of Galilee, why do you stand looking into heaven? This Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven." Then they returned to Jerusalem from the mount called Olivet, which is near Jerusalem, a sabbath day's journey away..." (Acts 1:1-12, RSV)
The Ascension, then, sets the stage for Pentecost. It also completes the Incarnation, the process by which humanity is united with Deity, the Deity of God the Son; God and humanity are forever joined. It but remains for that unity to be actualized in the lives of Jesus' followers by the "baptism in the Holy Spirit".
