 This is called the great exchange. Christ gives us his righteousness. We give him our unrighteousness. Christ gives us eternal life and salvation. We give him death and condemnation, which he endured on the cross. This is how Jesus fulfilled all righteousness. This is how he fulfilled everything written in the law and the prophets. He not only lived in obedience to God's righteous law, but he fulfilled every promise of God in order to give that righteousness to us.