I feel like there's no possible way I can do justice to these verses, especially verses 33 to 35, I’ve been sitting with them for over an hour this morning and I can't find the words to convey the magnitude of what's being said. Basically God is telling David that he will not change his mind, he won't go back on the promises made to him and his offspring, even if they disobey! They will bear the consequences of their disobedience, but his promises will still stand.
Why? Because of one special word in verse 34; covenant. Our God is covenantal, and to make a covenant with someone is no small thing. “Covenants in scripture are solemn agreements, negotiated or unilaterally imposed, that bind the parties to each other in permanent defined relationships, with specific promises, claims, and obligations on both sides (e.g., the marriage covenant, Mal.2:14).” (ESV Bible notes on Covenant p.30). It goes on to say; “when God makes a covenant with his creatures (us), He alone establishes its terms… God's covenant rests on his promise(s)…” (ESV notes p. 30).
And what has he promised here? To David he has said; “I will not remove my steadfast love from you, I will not be false to my faithfulness (I will not fail to keep my promises to him - NLT), I will not violate my covenant, I will not take back a single word I said (NLT), I will not lie to David…”. And if that isn't enough, he goes on to promise that his offspring and his throne will endure forever.
God doesn't just say it, he swears it, and he does so by the greatest element of his character, his holiness!
“Once for all I have sworn an oath by my Holiness; I will not lie to David.” (v. 35)
I absolutely love what Charles Spurgeon has to say regarding this verse;
“God here pledges the crown of his kingdom, the excellent beauty of his person, the essence of his nature. He does as good as say that if he ceases to be true to his covenant he will have forfeited his holy character. What more can he say? In what stronger language can he express his unalterable adherence to the truth of his promise?” (from Enduring Word online commentary).
God will never forfeit his holy character. The entire Old Testament is the repeated story of how he redeemed, rescued, and restored his people because of his holy character. His name and reputation were at stake and he would not forfeit those as well. He is the only one who has the right to swear by his name because he is the only one holy enough to do so.
So when we jump forward to Luke 1: 31-33 where the angel Gabriel repeats these words to Mary regarding the child she will bear, she knows deep within her that this is the truth. She knows because she has heard the words of the old testament, she knows the Psalm from which these words come.
The birth, life, death, and resurrection of Jesus instituted the new covenant but ultimately fulfilled; “The goal of God's covenantal dealings, as it always has been, the gathering and sanctifying of the covenant people, ‘from every nation, tribe, and tongue’ (Rev.7:9), who will one day inhabit the new Jerusalem…” (ESV notes). God the Father's goal has always been to have a people for himself; “they will be his people, and he will be their God” (Rev.21:3, Gen.17:7, Ex.29:45-46). But not just any people, a holy people, a chosen people, and because of Christ, because of his earthly life and death, we who are in him are those people.