Frustrated at the timeline, yet confident in God.
Ever been there?
David has … in fact, that’s what Psalm 13 is all about. As we’ve seen over the last few weeks, David is confident that the Lord will rescue him from his enemies and bring them under His judgment for their treason against David.
But David still isn’t seeing the Lord do what He has promised; thus, Psalm 13 is written. 
Yet this isn’t a depressing song, nor is it one filled with accusations against God. Rather, David petitions the Lord to act in covenant faithfulness. David is confident that the Lord will provide, but he is still looking at the enemies at the gate and wondering when God will move.
The question of, “How long?” that fills our hearts is one that is a common theme throughout the Bible - in fact, it goes all the way back to the heartbreak of Genesis 3, traces its way through Israel’s history, crescendos in the coming of Jesus, and is, even now, the song that we sing as Christians as we long for the second coming of Jesus. 
Thus, Psalm 13 is a song that ought to fill our mouths as God’s people, as we long for Jesus and strive to live in holiness as we wait for Him.