29“Fellow Israelites, I can tell you confidently that the patriarch David died and was buried, and his tomb is here to this day. 30 But he was a prophet and knew that God had promised him on oath that he would place one of his descendants on his throne. 31 Seeing what was to come, he spoke of the resurrection of the Messiah, that he was not abandoned to the realm of the dead, nor did his body see decay.
The undoubted aim of all the prophets was to take people by the hand and lead them to Christ.
God used an oath not only to help David believe, but also so the promise would be held in greater esteem. We also benefit from this oath. Clearly, the Lord shows how excellent the covenant is through this solemn oath.
Christ is called the Son of God, because he is eternal; and Christ is called the descendant of David, because he is human.