…it goes back to God’s Promise:
13 He will build a temple for my name) and I shall make his royal throne secure for ever.
16 Your dynasty and your sovereignty will ever stand firm before me and your throne be for ever secure." ’
25 ‘Now, Yahweh God, may the promise which you have made for your servant and for his family stand firm forever as you have said, 26 so that your name will be exalted for ever and people will say, “Israel’s God is Yahweh Sabaoth.” Your servant David’s dynasty will be secure before you, 27 since you, Yahweh Sabaoth, the God of Israel, have disclosed to your servant, “I am going to build you a dynasty.” Hence, your servant has ventured to offer this prayer to you. 28 Yes, Lord Yahweh, you are God indeed, your words are true and you have made this generous promise to your servant. 29 What is more, you have deigned to bless your servant’s dynasty, so that it may remain for ever before you; for you, Lord Yahweh, have spoken; and may your servant’s dynasty be blessed with your blessing for ever.’ (2 Samuel 7:13, 16, 25-29)
…the only way David’s throne/dynasty could endure forever would be if an Eternal King would possess it; conversely, the only way that God’s Promise would come into fruition would be if one of David’s descendants could occupy the David’s throne forever!
Jesus is the Eternal King of kings and Lord of lords!