When David affirms that the Lord is God and that his Word his trustworthy, he honours the Lord. The first commandment calls on God’s people to have no other gods before him; they must trust the Lord alone to care for them and know that he will do as he says. David responds rightly to the Lord with this trust and confidence. He knows what God has promised will come to pass.1
28 And now, O Lord GOD, you are God, and your words are true, and you have promised this good thing to your servant.