These are the two parts of justification. The first is grace revealed through Christ, that through Christ we have a gracious God, so that sin can no longer accuse us, but our conscience has found peace through trust in the mercy of God. The second part is the conferring of the Holy Spirit with His gifts, who enlightens us against the defilements of spirit and flesh (2 Cor. 7:1). Thus we are defended against the opinions with which the devil seduces the whole world. Thus the true knowledge of God grows daily, together with other gifts, like chastity, obedience, and patience. Thus our body and its lusts are broken so that we do not obey them. Those who do not have this gift or do not use it this way, but fall into the uncleanness of either the flesh or the spirit, so that they approve of all doctrines without discrimination – they are dominated by the flesh, and they do not know the bath of the Holy Spirit for which David is asking here.
Martin Luther commenting on Psalm 51:2
Luther’s Works v. 12: Selections from the Psalms 331