Wiersbe points out that Nathan had the privilege of being God's choice to present the covenant with David and now has the heavy responsibility of dealing with David's sin.
What this brings to mind for me is that God is the I am. All time is the same for Him. He knew when He sent Nathan with the covenant that He would be sending Nathan back with the judgement. And yet He still sent Him with the covenant. That blows my mind. As He is lifting David up he was experiencing the disappointment of the ultimate and permanent state of spoiler alert. He knows we are going to blow it and blow it big, even on our worst day. It's mind blowing; but it is comforting. He knew Jesus was going to pay for all of those sins so that we can return to and remain in communion with our Lord.
Praise the living God. Grace and mercy in one painful scene.