“Out of the depths” can refer to a variety of low places in life—failure, pain, sin, etc. From this low place, God can bring the “abundant redemption” that sweetly sings out at the end of this chapter.
Imagine waiting through the night as a watchman with no wristwatch.
As the vigilant watchman stays up through the night longing to see the light of morning, this psalm speaks of a soul that even more desperately longs for God.
May our souls so long for the light of God!