Let me sum it up in this way, therefore. You and I – and to me this is one of the great discoveries of the Christian life; I shall never forget the release which realizing this for the first time brought to me – you and I must never look at our past lives; we must never look at any sin in our past life in any way except that which leads us to praise God and to magnify his grace in Christ Jesus.
I challenge you to do that.
If you look at your past and are depressed by it, if as a result you are feeling miserable as a Christian, you must do what Paul did. ‘I was a blasphemer,’ he said, but he did not stop at that. Does he then say, ‘I am unworthy to be a preacher of the gospel’? In fact he says the exact opposite: ‘I thank Christ Jesus our Lord who hath enabled me,for that He counted me faithful putting me into the ministry, etc.’ When Paul looks at the past and sees his sin he does not stay in a corner and say: ‘I am not fit to be a Christian, I have done such terrible things.’ Not at all. What it does to him, its effect upon him, is to make him praise God. He glories in grace and says: ‘And the grace of our Lord was exceeding abundant with faith and love which is in Christ Jesus.’
D. Martyn Lloyd-Jones, Spiritual Depression: Its Causes and Cure (Grand Rapids: Eerdmans, 1965), 75.