2 Samuel 12:12 - Matthew Poole's English Annotations on the Holy Bible

I will do this thing, i.e. I will execute this judgment. This God did by inclining David's heart to leave his concubines to keep his house, and so to come into Absalom's power; by giving up Ahithophel to his own carnal policy, which readily suggested to him that wicked and desperate counsel; and by exposing Absalom to these temptations, and leaving him to his own vicious inclinations, which God certainly knew would in such circumstances produce that effect. So the sin was wholly from men, but the ordering and overruling their mistakes and miscarriages to this end was from God.