Charles Ellicott Commentary Psalms 66:18

"If I regard iniquity in my heart, The Lord will not hear:" — Psalms 66:18 (ASV)

If I regard ... —Rather, if I had seen evil (that is, had had it purposely in view) in my heart, the Lord would not have heard me. One may not “be pardoned and retain the offence.” The reference may be either to the forming of wicked schemes, or to the complacent view of wickedness in others.

The protestation of innocence in this verse, being made by or for the community at large, marks a late period for the composition. (See Introduction, and Psalm 44:0, Introduction and Notes.)