“The Christian is a man who says, ‘Yes, alas, it is true; I have been vile and horrible and a desperate sinner, yet I believe I stand righteous in the presence of God in Christ.’ He can face his past, he can look into himself and see the vileness, the pollution, of sin still remaining, and when the devil says, ‘Do you think you have a right to say that you are a Christian?’, he says, ‘Yes, I do. In spite of the fact that all this is true of me, I know I am righteous in Christ.’ He does not look at himself to find justification, he looks entirely out to Christ and all that he is in Christ. He believes this Word about the resurrection, the proclamation of God in raising Christ from the dead. He looks to that in spite of all. If you cannot do that you have not got justifying faith.
Faith is this confident protest against every voice that assails us from within and from hell. It stands with Paul in chapter 8 and says, ‘Who shall lay anything to the charge of God’s elect? It is God that justifieth.’ Who is he that condemneth in the light of that? There is no one, there is nothing. It is in spite of what we know about ourselves, of what the Law knows about us, of what hell knows about us. So stop talking about your past sins, stop talking about your present sinfulness. In this matter of justification you must not mention them. You just stand as you are in the righteousness of Jesus Christ, and in Him believe the staggering Word of God about yourself.”
Martyn Lloyd-Jones, Romans: Atonement and Justification, Exposition of Chapters 3:20-4:25, pp. 248-249).