If, in your justification, God once-for-all forgave the guilt of all your sins — past, present, and future — then why do you still need to confess your sins?
Kevin DeYoung writes:
You often hear statements like this: “There is nothing you can do to make God love you more or to make him love you less.” And while it’s true that those who have been justified by grace through faith can never be more justified, we can hear a statement like this incorrectly. Yes, God loves us fully in Christ, but this does not mean we are incapable of doing things that are displeasing to God. We can get out of step with the Spirit. We can grieve him too. Even after we have been redeemed, our sin continues to be offensive to God. And this has an effect.