Psalm 119:123 is a little tricky: “My eyes fail, looking for your salvation, looking for your righteous promise.” Is the psalmist despairing and at the end of his hope or is he yearning intensively? The Hebrew word here (qalah) can mean either “completed” and could connote “totally focused on” or, which is how most translations proceed, “exhausted, come to the end.” I think the latter sense is probably right.
The psalmist yearns in hope and he is coming to the end of his strength. He isn’t sure how much longer he can go on.
His focus and yearning, in the midst of his oppression, is on the just word of God — God’s promise to bless those who observe his Torah. How much longer can he go on? He’s pressed on to the end to see the “just word” — the promise of victory.
I like this: in vv. 121-122, we see a confident appeal on the basis of his integrity; in v. 123 he comes to the bottom of himself, he recognizes that he can’t go on without God’s help. Not in the sense that he finds his disposition in 121-122 wrong, but in the sense that he is wearing down, admitting that it is hard at times to press on in a forward direction.