"God forgives you now you need to forgive yourself." Without further qualification this statement is no help to the Christian. If told to a non-Christian it is a lie.
"I have continually had such a sense of my sinfulness as would sink me into utter despair, if I had not an assured view of the sufficiency and willingness of Christ to save me to the uttermost. And at the same time I had such a sense of my acceptance through Christ as would overset my little bark, if I had not ballast at the bottom sufficient to sink a vessel of no ordinary size." (Charles Simeon, Moule 134f.)
The fact is, we must not forget our sins or forgive ourselves. It would be better if we remembered our sins and sinfulness because when considered alongside Jesus it makes the sight of Him that much more sweet, for in His justice He has chosen to forgive the sins of those who believe. It is hard to imagine being owed anything or to have feelings of self-sufficiency if we are constantly reminded that we are poor, wretched, sinful beings with no hope besides Jesus. Intimate relationship with Christ illuminates our wretchedness and without His love for us we would crumble under the weight of it. If we were given a perfect view of our sinful state in comparison with God's holiness we would be undone and paralyzed, unable to do anything. (Numbers 17:12-13) Yet, because of the freedom that comes from His grace to us through faith in Jesus Christ we are able to see our terrible state and function. Though we are wretched and can do nothing without Him He is in us working His will through us. (Colossians 1:27)
Let your sin and sinfulness be the ballast at the bottom of your ship and let Christ's salvation and grace to you be the sail and the wind that propels you for His glory.
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See also: Brothers, We Must Not Mind a Little Suffering: Meditations on the Life of Charles Simeon by John Piper