My soul also is greatly troubled.
But you, O Lord—how long?
Turn, O Lord, deliver my life;
save me for the sake of your steadfast love.
Sometimes it feels like God is taking His time with something that I think I need an answer on RIGHT NOW! My feelings can then lead me to questions about God. That seems to be where David is with this psalm. He is emotionally worked up. He is running His life on his feelings. So in desperation he cries out a two word question to God: "How long?"
Even in this difficult moment, David does not let emotion rule his heart completely. There is an immediate turn to faith in what he knows about God. Theology saves the day from emotional instability. David once again offers his request, this time appealing to the Lord's overwhelming grace: "save me for the sake of your steadfast love."
There is a shift going on here that needs to be clearly applied during times of emotional crisis. David deliberately shifts his thoughts away from his feelings and toward the character of God. He goes from "How long, O Lord?" to focusing on asking God to act for the sake of God's own grace and not David's feeling of need. He stops questioning God and instead trusts that God will be God. There is a big difference in those two attitudes. The first attitude flirts with unbelief and selfish thinking. The second attitude is real, gutsy faith.
I do love that this psalm shows us both sides of the struggle in two verses side by side. I find hope in that observation. God can handle our humanity, our struggles to believe Him, our falls into emotional selfishness. He hears our prayers even when we are struggling to work out faith. And God remains steadfast in His love even when we waver in ours.