Why Do I Still Sin If I'm a Christian?

If becoming a Christian meant sin simply stopped, every honest believer would have to conclude he isn’t one. But that is not what Scripture promises, and the gap between the Christian you want to be and the Christian you actually are is not proof that something has gone wrong. It is, strange as it sounds, a mark of spiritual life.

Lutherans describe the Christian with a phrase from Luther: simul iustus et peccator—at the same time righteous and sinner. In Christ you are fully righteous, clothed in His perfect record, right now. And in yourself you remain a sinner, with a fallen nature that will not be fully put to death until you are. Both are completely true at once. So the Christian life is not a smooth climb out of sin into sinlessness; it is a daily war between the new person the Spirit has created and the old flesh that keeps clawing its way back.

Paul—an apostle—describes this war in the present tense: “the good I want to do, I do not do” (Romans 7:19); the flesh and the Spirit are “opposed to each other,” so that you cannot simply do as you please (Galatians 5:17). Notice who is fighting. Only a living Christian feels this struggle at all. The unbeliever is not at war with his sin; he is at peace with it. The very fact that your sin grieves you—that you fight it, and keep returning to confess it—is itself evidence that the Spirit is at work in you. Dead men do not struggle.

So take the battle seriously, but do not let it drive you to despair, or to the false hope of a “victorious” life free of all sin this side of heaven. Sanctification is real, and the Spirit truly changes us—but it is gradual, partial, and lifelong, and it never graduates you out of needing the Gospel. Each day you return to your Baptism: the old man drowned, the new man raised forgiven. The struggle is not failure. It is the shape of faith on the way home.