A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 130:1The penitent sinner's hope is in God's mercy only. (Psa 130:1-8)
depths--for great distress (Psa 40:2; Psa 69:3).
psa 130:3shouldest mark--or, "take strict account" (Job 10:14; Job 14:16), implying a confession of the existence of sin.
who shall stand-- (Psa 1:6). Standing is opposed to the guilty sinking down in fear and self-condemnation (Mal 3:2; Rev 6:15-16). The question implies a negative, which is thus more strongly stated.
psa 130:4Pardon produces filial fear and love. Judgment without the hope of pardon creates fear and dislike. The sense of forgiveness, so far from producing licentiousness, produces holiness (Jer 33:9; Eze 16:62-63; Pe1 2:16). "There is forgiveness with thee, not that thou mayest be presumed upon, but feared."
psa 130:5wait for the Lord--in expectation (Psa 27:14).
watch for, &c.--in earnestness and anxiety.
psa 130:7Let Israel, &c.--that is, All are invited to seek and share divine forgiveness.
from all his iniquities--or, "punishments of them" (Psa 40:12, &c.).