Psalm 119:43 is odd: “Never take your word of truth from my mouth, for I have put my hope in your laws.” My rabbi commentary, by Samson Hirsch, says this: “Do not make it appear as if my mouth had said something entirely untrue when I pointed out Thy righteous ordinances to my opponents.”
This is what I meant when I said the psalmist thinks God cares about everything he does and says. His God cares about everything.
His care here is for eloquence or at least clarity; his fear is getting tongue-tied or confused when he is on the spot about the mishpatim, the commandments. He simply prays to be simply clear when he speaks about what he believes and what he observes.
Frankly, I struggle to think of a context for this kind of prayer for the psalmist: Is he being called on the spot for his understanding of Torah? of the kind of observance he is committed to?
Not sure, but the psalmist knows God cares.