By that will we have been sanctified through the offering of the body of Jesus Christ once for all. Once for all. Not every day anew. Not after every mistake back to square one. One offering. Once. Done.
Sanctification in the New Covenant is not a process you must work through. You are sanctified, that is your status. Not because you live holy, but because his offering is sufficient. Your standing before God depends on Christ, not your daily performance.
This is both liberating and challenging: If you are already sanctified, then you no longer live for sanctification but from sanctification.