Self-righteousness is like a bottomless cup: though you pour and pour, you will never be able to fill it. Why? Because pouring yourself into yourself adds nothing to you. Nothing plus nothing always equals nothing. Instead, accept God’s righteousness rather than trying to accumulate your own. You will find that the righteousness he offers is real. And that is what fills the cup of sanctification.
Baker Books, 1500 Illustrations for Biblical Preaching, by Michael P. Green