Out with the Old, In with the New

Life in Christ isn't just a 'do or don't' thing. In other words, do this, or don't do this, and you'll be accepted. More accurately it's an 'in or out' thing.

Either you are in Christ or you are not. It's being in Christ that gives you the freedom to do the things that are pleasing to Him because it's His life lived through you.
So when you are in sin, and struggling to believe, the true cure is bringing your sin and unbelief to Jesus, letting Him deal with it and change you from within.