The expression “from the depths” connotes “deep water”, and this is a metaphor for the dire straits in which the worshipper finds himself. The psalm describes a person who is praying because he feels that he is about to drown; thus, God’s aid is a vital and immediate need.

The “depths” in which the worshipper finds himself, and from whence he called to God, are a metaphor for his sins.

However, the great distress which the worshipper suffered in stanza a. is eased somewhat once he has given thought, in stanza b., to the well-known truth that “with God is forgiveness." Now he is certain that God has indeed heard his voice and has listened to his supplications.

Courtesy of the Virtual Beit Midrash, Yeshivat Har Etzion