“…when the devil comes and says, ‘You have no standing, you are condemned, you are finished’, you must say, ‘No! my position did not depend upon what I was doing, or not doing; it is always dependant upon the righteousness of the Lord Jesus Christ.’ Turn to the devil and tell him, ‘My relationship to God is not a variable one. The case is not that I am a child of God, and then again not a child of God. That is not the basis of my standing, that is not the position. When God had mercy upon me, He made me His child, and I remain his child. A very sinful, and a very unworthy one, perhaps, but still his child!
And now, when I fall into sin, I have not sinned against the law, I have sinned against love. Like the prodigal, I will go back to my Father and I will tell Him, “Father, I am not worthy to be called your son.” But He will embrace me, and He will say, “Do not talk nonsense, you are My child,” and He will shower his love upon me! That is the meaning of putting on the breastplate of righteousness! Never allow the devil to get you into a state of condemnation. Never allow a particular sin to call into question your standing before God. That question has been settled.”
Martyn Lloyd Jones, The Christian Soldier, p. 255