The first account I made, Theophilus, was [a continuous report] about all the things that Jesus began to do and to teach [Luke 1:1-4] until the day when He ascended to heaven, after He had by the Holy Spirit given instruction to the apostles (special messengers) whom He had chosen. To these [men] He also showed Himself alive after His suffering [in Gethsemane and on the cross], by [a series of] many infallible proofs and unquestionable demonstrations, appearing to them over a period of forty days and talking to them about the things concerning the kingdom of God. While being together and eating with them, He commanded them not to leave Jerusalem, but to wait for what the Father had promised, “Of which,” He said,“you have heard Me speak. [John 14:16, 26; 15:26] For John baptized with water, but you will be baptized and empowered and united with the Holy Spirit, not long from now.”
So when they had come together, they asked Him repeatedly, “Lord, are You at this time reestablishing the kingdom and restoring it to Israel?” He said to them, “It is not for you to know the times or epochs which the Father has fixed by His own authority. But you will receive power and ability when the Holy Spirit comes upon you; and you will be My witnesses [to tell people about Me] both in Jerusalem and in all Judea, and Samaria, and even to the ends of the earth.”
And after He said these things, He was caught up as they looked on, and a cloud took Him up out of their sight. While they were looking intently into the sky as He was going, two men in white clothing suddenly stood beside them, who said, “Men of Galilee, why do you stand looking into the sky? This [same] Jesus, who has been taken up from you into heaven, will return in just the same way as you have watched Him go into heaven.”