It’s about calling out to God from the depths of a sense of guilt and found forgiveness in God’s great mercy. This psalm is by some thought to have been written by David either when persecuted by Saul, and in great distress. In the slightly different numbering system used in the Greek Septuagint version of the Bible, and in the Latin Vulgate, this psalm is Psalm 129. The New American Bible Revised Edition (2010) divides the psalm into two parts: verses 1-4 are a cry for mercy; verses 5-8 are a model expression of trust in God.

It reads in Psalm 130:1-8 NIV:
A song of ascents.
Out of the depths I cry to you, Lord; Lord, hear my voice. Let your ears be attentive to my cry for mercy. If you, Lord, kept a record of sins, Lord, who could stand? But with you there is forgiveness, so that we can, with reverence, serve you. I wait for the Lord, my whole being waits, and in his word I put my hope. I wait for the Lord more than watchmen wait for the morning, more than watchmen wait for the morning. Israel, put your hope in the Lord, for with the Lord is unfailing love and with him is full redemption. He himself will redeem Israel from all their sins.