With this specific phrase Peter is referencing another Psalm, Psalm 132:11. Psalm 132 focuses on the promise which God made to David in 2 Samuel 7:12–13. God promised David that one of his descendants would sit on the throne to rule over Israel. The promise was not for a perpetual line of descendants but a single descendant to come.1 Peter argues that King David saw, in advance, that one of his descendants would be the Holy One that God places on his throne and he would also experience the miracle of a resurrection from the dead.2 With Christ having been resurrected, this promise must be a reference to him and thus it has also been fulfilled.3
30 Being therefore a prophet, and knowing that God had sworn with an oath to him that he would set one of his descendants on his throne,