We become numb to sin when we treat Jesus as a sin manager rather than as the one who paid our sin debt.
1 Have mercy on me, O God,
according to your steadfast love;
according to your abundant mercy
blot out my transgressions.
2 Wash me thoroughly from my iniquity,
and cleanse me from my sin!
3 For I know my transgressions,
and my sin is ever before me.
4 Against you, you only, have I sinned
and done what is evil in your sight,
so that you may be justified in your words
and blameless in your judgment.
5 Behold, I was brought forth in iniquity,
and in sin did my mother conceive me.
6 Behold, you delight in truth in the inward being,
and you teach me wisdom in the secret heart.
7 Purge me with hyssop, and I shall be clean;
wash me, and I shall be whiter than snow.
1 John 1:8-9
8If we say we have no sin, we deceive ourselves, and the truth is not in us. 9If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.