But I have trusted in your steadfast love; my heart shall rejoice in your salvation. I will sing to the Lord, because he has dealt bountifully with me. Psalm 13:5-6 (ESV)
The Psalms are full of laments, many of which begin with the phrase, "How long, O Lord?" These verses from Psalm 13 immediately follow one such passage, but there is a noticeable shift in tone, beginning with the word "but."