King Abimelech vs. King David?

Abimelech king of the Philistines didn’t sin

Even though he saw “Isaac was caressing his wife Rebekah”

And called him and said, “Behold, certainly she is your wife!

How then did you say, 'She is my sister'?  …

What is this you have done to us?  One of the people might easily have lain with your wife,

and you would have brought guilt upon us” (Gen. 26:8-10).

However, David king of Judah sinned and had done what was evil in the sight of the Lord

When he saw very beautiful in appearance Bathsheba, the wife of the loyal solider Uriah,

bathing and laid with her and when she was pregnant,

David tried to cover it up even by killing Uriah (2 Sam. 11).