Adam Clarke on Acts 1:11

Gazing up into heaven - Not to the top of a mountain, to which an unbridled fancy, influenced by infidelity, would intimate he had ascended, and not to heaven.

This same Jesus - Clothed in human nature, shall so come in like manner - with the same body, descending from heaven by his sovereign and all-controlling power, as ye have seen him go into heaven. Thus shall he come again to judge the quick and the dead. It was a very ancient opinion among Christians, that when Christ should come again to judge the world he would make his appearance on Mount Olivet. Some think that his coming again to destroy the Jewish nation is what the angels refer to. See a connected account of the different appearances of Christ at the end of this chapter.