knowing that God had sworn with an oath to him
The Throne of His Father David
Psalm 132:11 The Lord hath sworn in truth unto David; he will not turn from it; Of the fruit of thy body will I set upon thy throne.
Luke 1:32 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
Acts 2:30 Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne;