Piper on justification and sanctification
“The only sin we can fight against successfully is a forgiven sin”:
All the sins of God’s people, past, present and future, are forgiven because of the death of Christ once for all. . . . This justification on the basis of Christ’s death for us is the foundation of sanctification — not the other way around. I put it like this: the only sin we can fight against successfully is a forgiven sin. Without a once-for-all justification through Christ, the only thing that our striving for holiness produces is despair or self-righteousness.
But I did not say that the work of God in justification makes the work of God in sanctification optional. I didn’t say (the Bible doesn’t say) that forgiveness makes holiness optional. It doesn’t make it optional, it makes it possible. What we will see today is that the God who justifies also sanctifies. The faith that justifies also satisfies — it satisfies the human heart and frees it from the deceptive satisfactions of sin. Faith is the expulsive power of a new affection (Thomas Chalmers). That is why justification and the process of sanctification always go together. They both come from the same faith. Perfection comes at the end of life when we die or when Christ returns, but the pursuit of holy living begins with the first mustard seed of faith. That’s the nature of saving faith. It finds satisfaction in Christ and so is weaned away from the satisfactions of sin.
— John Piper, God Sanctifies His People