I've been going to school on Michael Horton's stiff challenge to contemporary Christians regarding a moralizing, try-harder approach to Christianity rather than leaning on the grace of God. Perhaps because I will soon speak on Peter's denial the quote below caught my eye.
Before singing, "What a Friend We Have in Jesus," I find myself, with Peter, saying, "Depart from me, for I am a sinful man." (Luke 5:8). And Peter did not feel this only once, when he first met Jesus. His journey with Jesus fluctuated from high points, such as his confession of Jesus as the Christ, to the low point of denying Christ three times, back to the high point of being martyred for his testimony to his Savior. Like Peter, our Christian life is a roller coaster of faithfulness and unfaithfulness. Since we always draft back to self-confident triumphalism (remember Peter's protest, "i will never deny you!" just before he did,) we need to hear God's verdict on our righteousness through the law and his assurance of pardon in the gospel." Jesus example is not good news but a terrifying burden unless he is first of all the one who saves me from my inability to follow it."
Michael Horton, Christless Christianity, p. 135-136.