Acts 2:34

For David ascended not into the heavens: but he saith himself, The Lord said unto my Lord, Sit thou on my right hand, Till I make thine enemies the footstool of thy feet.

This quotation from Psalms 110:1 indicated: (1) that the Son of David would also be the Lord of David (Matthew 22:43ff), and (2) that the Son of David would sit on the right hand of God, an idiomatic promise of the ascension into heaven. Peter did not have to prove that David himself had not ascended to heaven, for his grave was still in Jerusalem. In post-apostolic times, Jewish commentators have attempted to deny the Davidic authorship of this Psalm, with a view to softening the argument here; but the Lord Jesus himself left no doubt whatever of it, naming David as the author (Matthew 22:43).

Having thus established a number of the most important truths regarding Christianity, especially the power and godhead of Jesus Christ, his resurrection from the dead, ascension into heaven, and sitting down upon the throne of David in heaven, and the fact of Christ's having poured forth the Holy Spirit in such a divine demonstration as the multitude had witnessed, Peter then announced his conclusion.