Psalms 51:1b

Have mercy on me, O God,

according to your unfailing love;

according to your great compassion

blot out my transgressions.

(v1, NIV)

David asks for his transgressions to be blotted out. It's as if all he has ever done has been written in a book. David is asking for this record that has been written down to be erased in some way. He wants for it to be blotted out so that it would be as if it never happened. Often times after having sinned, I desperately wish for my sins to be blotted out. I wish to have never done them. I wish to go back in time and undo what I had done. David asks God for this and pleas for this according to God's compassion. In the ESV, the word used is mercy. David is appealing to God's mercy or compassion to blot out his transgression. With sin comes punishment, and God's mercy may kindly withhold it from us by blotting out our transgressions in some way. In addition, if it weren't for his compassion for us, he wouldn't have much reason to even want to blot out our transgressions.