I acknowledge my transgressions; and my sin is ever before me. David, Psalm 51:3
Does this verse present a cog in the mechanism of grace for you? Does it keep you wavering back and forth between the obligation to remember your sins and freedom to rest in the reality that Christ has done away with them? Yeah, yeah, I know the supposed godly reasoning as to the benefits of keeping a healthy awareness of one's sins, however, why would God expect you to remember the very thing he has forgotten? But what then of David? Are we to ignore what the Spirit of God taught him? Not so. Instead, I suggest we listen very carefully.
As to this salvation, the prophets who prophesied of the grace that would come to you made careful searches and inquiries, seeking to know what person or time the Spirit of Christ within them was indicating as He predicted the sufferings of Christ and the glories to follow. It was revealed to them that they were not serving themselves, but you, in these things which now have been announced to you through those who preached the gospel to you by the Holy Spirit sent from heaven--things into which angels long to look. 1 Peter 1:10-12
Consider that David was one of those who prophesied of the grace that would come to you and me. For regarding this salvation he made careful searches and inquiries in hopes of understanding, among other things,
...the blessing on the man to whom God credits righteousness apart from works Romans 4:6
That's right, he understood the concept of such forgiveness but not its reality. And as a man under law, he only knew the fleeting righteousness of works. He desired the blessing of having righteousness credited apart from works. He desired to know the real forgiveness that would one day be proclaimed through Christ.
While we might read Psalm 51 as a pattern for those in Christ to follow, David had recorded the cry of a heart that could not comprehend the fortune WE now have in Christ.
Blessed are those whose lawless deeds have been forgiven, and whose sins have been covered. Blessed is the man whose sin the Lord will not take into account. Romans 4:7-8, as quoted from Psalm 32:1-2
Why do we listen to those who present grace as a mechanism that breaks down under the strain of that which Christ has removed? If you want to honor the Spirit that moved David, stand firm in the fortune that he desired to understand: Christ in you, the hope of glory.