Psalm 143:2 And enter not into judgment with thy servant: For in thy sight shall no man living be justified.
David asks God not to judge him. He knows that God would never see him as justified or right. There is nothing in David that would make God approve of Him. David has sinned and he knows it. No one could ever make themselves right with God.
That is why God has done such wonderful things in our lives. He has made us a new creature. He has made us partakers of the divine nature. He has taken our sins on Himself and made us the righteousness of God in Him.
He sees us perfectly. We stand before Him as new creatures. We would never have been able to stand if He had not done so much in our lives. We are no longer men but sons of God!