Martin Luther once wrote to a young friend of his who was struggling with guilt and failure:

When the devil throws our sins to us and declares that we deserve death and hell, we ought to speak thus: “I admit that I deserve death and hell.  What of it?  Does this mean that I shall be sentenced to eternal damnation?  By no means.  For I know One who suffered and made satisfaction in my behalf.  His names is Jesus Christ, the Son of God.  Where He is, There I shall be also.”

Excerpt from Michael Reeves book: Rejoicing in Christ, pg. 63.