The true way to Christianity is, first, to acknowledge that we are sinners according to the law and that it is impossible for us to do anything good.- Martin Luther

The true way to Christianity is, first, to acknowledge that we are sinners according to the law and that it is impossible for us to do anything good. Therefore, you cannot earn grace by what you do; if you try, you double your offense, for since you are a bad tree, you can only produce bad fruit—that is, sins (see Matthew 7:17; Romans 14:23). Anyone who wants to merit grace by works before having faith is trying to please God with sins, which is nothing but heaping sin upon sin and mocking God and provoking his wrath. When a person is taught this by the law, he is terrified and humbled and sees the magnitude of his sin and cannot find in himself one spark of the love of God. Therefore, he confesses that he is guilty of death and eternal damnation. The first part of Christianity, then, is the preaching of repentance and self-knowledge.

The second part is this: if you want to be saved, you must not seek salvation through works. God has sent his one and only Son into the world, that we might live through him. He was crucified and died for you and bore your sins in his own body. God has revealed to us by his Word that he will be a merciful Father to us, and without our deserving it (since we can deserve nothing good) he will freely give us remission of sins, righteousness, and everlasting life for the sake of Christ his Son. God gives his gifts freely to everybody, and that is the praise and glory of his divinity. Those who will not receive grace and everlasting life from him freely but want to earn them by their own actions would in this way utterly remove the glory of his divinity. Therefore, so that he may maintain and defend this glory, he is obliged to send his law, like lightning and thunder from heaven, to bruise and break those hard rocks.

Martin Luther – Galatians (Crossway Classic Commentaries)