This recognition of God's grace as we pursue holiness ... frees us from believing that our sins could separate us finally from his love. All too often we are motivated to live by our guilt, rather than by God's grace. We recognize our failings, we feel the conflict within us because of our remaining corruption, we know the oppositions of Satan and we hear his accusations ringing loudly in our ears "You call yourself a Christ and you did that? You screamed at your children or at your spouse. You envied your co-worker's success to such a degree that you sought to sabotage his rise up the ladder. You shaded the truth so that it became a lie, and you did it to make yourself look good. You lusted in your heart and dreamed about having someone else's spouse." What we tend to do with these accusations is to use them as a motivation to make amends, to placate God with promises of repentance and good behavior. We fear God's response to our sins; we fear that he will walk all over us, with his God-sized cleats. We are like children who fear our parents' discipline, but not our parents' distress. Ad so, we use this guilt not to drive us to Christ and his mercy, but to drive us to self-righteous achievement. We begin to measure our spirituality by what we don't do, what sins and transgressions we avoid, and what external righteousness we manage to accomplish. All of this we do as an attempt to keep god happy with us. Meanwhile, we are far from communion with him, far from a deep love for him, and far indeed from understanding there grace and mercy of God."
Page 45-46 of "On Being Presbyterian.