"What happens when I make a mistake or sin? You are still the righteousness of God in Christ Jesus and not under the law."
Rob Rufus
"God did it for us. Out of sheer generosity He put us in right standing with Himself. A pure gift. He got us out of the mess we're in and restored us to where He always wanted us to be. And He did it by means of Jesus Christ."
Romans 3:24
God's arms are always open to us, but it's sometimes difficult to see that when we fail. So God has given us Christ's righteousness (right standing with God) to be our own. This is a righteousness that is totally apart from and unaffected by our behavior. Even if we fail, we are still right with God, still righteous, because our rightness is based on Christ's behavior, which is perfect. That is why He gave us this gift of Christ's goodness and rightness, so we can come to God without shame or fear, even when we fail!
A thought: My sin doesn't change His righteousness in me!