Luther says that if we obey God’s law without a belief that we are already accepted and loved in Christ, then in all our good deeds we are really looking to something more than Jesus to be the real source of our meaning and happiness. We may be trusting in our good parenting or moral uprightness or spiritual performance or acts of service to be our real and functional “saviors.” If we aren’t already sure God loves us in Christ, we will be looking to something else for our foundational significance and self-worth. This is why Luther says we are committing idolatry if we don’t trust in Christ alone for our approval.
The first commandment is foundational to all the other commandments. We will not break commandments two through ten unless we are in some way breaking the first one by serving something or someone other than God. Every sin is rooted in the inordinate lust for something which comes because we are trusting in that thing rather than in Christ for our righteousness or salvation. We sin because we are looking to something else to give us what only Jesus can give us. Beneath any particular sin is the general sin of rejecting Christ’s salvation and attempting our own self-salvation.
The best way of casting out an impure affection is to admit a pure one . . . It is only when, as in the gospel, acceptance is bestowed as a present, without money and without price, that the security which man feels in God is placed beyond the reach of disturbance. Only then can he repose in him as one friend reposes in another . . . The only way to dispossess the heart of an old affection is by the expulsive power of a new one.