Let us remember that our justification means not only that our sins are forgiven and that we have been declared to be righteous by God Himself, not merely that we were righteous at that moment when we believed, but permanently righteous. For justification means this also, that we are given by God the positive righteousness of His own Son, the Lord Jesus Christ. That is what justification means. It does not only mean that your sins are forgiven, but much more. It means that He clothes us also with the righteousness of Jesus Christ. He says in effect: `You are righteous; I see, not a sinner, but a righteous child of My own; I see you in Christ covered by His holiness and righteousness’. And when God does that to us, He does it once and for ever. You are hidden, you yourself and your whole personality and life stand in the righteousness of Christ before God. I say, therefore, with reverence and on the authority of the Word of God that God sees your sins no more; He sees the righteousness of Christ upon you. Lay hold of that.
Martyn Lloyd-Jones in Spiritual Depression: Its Causes and Its Cure
Martyn Lloyd-Jones on Justification