“What makes sin sin, what makes it so profoundly heinous, what makes it so deeply repugnant and culpable, is that it is offense against God. We dare not forget that the first commandment, according to Jesus, is the commandment to love God with heart and soul and mind and strength.
Thus the first sin– first sequentially, first in fundamental importance– is not to love God with heart and soul and mind and strength. It is the sin we always commit when we commit any other sin. At the most profound level, whenever we sin, God is always the most offended party.
David understands this: ‘Against you, you only, have I sinned and done what is evil in your sight’ (Psalm 51:3). And that is why, whatever other forgiveness we try to secure, we must have God’s forgiveness, or we have nothing.
Yes, you and I need to forgive one another. Yet in the most profound analysis of what sin is, only God can forgive sin.”
–D.A. Carson, Scandalous: The Cross and Resurrection of Jesus (Wheaton: Crossway, 2010), 159-160.