May the depth of His mercy engulf the depth of my sin!

The quote below is from John Calvin as he discusses the complete impossibility of confessing all our sins to God.  Instead of trying, we must throw ourselves upon the mercy of God!  But still, notice the last highlighted sentence and beyond, he does not say that believers must not admit and repent of our sin which we are aware of, simply that we must not consider that to be essential to our forgiveness, which would be to dishonor the sufficiency of Christ's work and steal peace from our consciences, as Calvin speaks of in 3.4.27.

"For, while they are wholly occupied with the enumeration of their sins, they lose sight of that lurking hydra, their secret iniquities and internal defilements, the knowledge of which would have made them sensible to their misery.  But the surest rule of confession is, to acknowledge and confess our sins to be an abyss so great as to exceed our comprehension. On this rule we see the confession of the publican was formed, "God be merciful to me, a sinner" (Luke 18:13); as if he had said, How great, how very great a sinner, how utterly sinful I am! the extent of my sins I can neither conceive nor express.  Let the depth of thy mercy engulf the depth of sin! What! you will say, are we not to confess every single sin? Is no confession acceptable to God but that which is contained in the words, "I am a sinner"?  No, our endeavor must rather be, as much as in us lies, to pour out our whole heart before the Lord. Nor are we only in one word to confess ourselves sinners, but truly and sincerely acknowledge ourselves as such; to feel with our whole soul how great and various the pollutions of our sins are; confessing not only that we are impure, but what the nature of our impurity is, its magnitude and its extent; not only that we are debtors, but what the debts are which burden us, and how they were incurred; not only that we are wounded, but how numerous and deadly are the wounds. When thus recognizing himself, the sinner shall have poured out his whole heart before God, let him seriously and sincerely reflect that a greater number of sins still remains, and that their recesses are too deep for him thoroughly to penetrate. Accordingly, let him exclaim with David, "Who can understand his errors? cleanse thou me from secret faults," (Ps. 19: 12.)" (Calvin's Institutes, 3.4.18, page 418; emphasis mine)

If you want to read more, you can find section 18 part way down this page.