On April 25, 1951, as a 53-year-old who had 12 years of life left,
C. S. Lewis discovered forgiveness.
In December of that year, he wrote to his priest (in Latin):
. . . during the past year a great joy has befallen me. Difficult though it is, I shall try to explain this in words. It is astonishing that sometimes we believe that we believe what, really, in our heart, we do not believe.
For a long time I believed that I believed in the forgiveness of sins. But suddenly (on St. Mark's Day) this truth appeared in my mind in so clear a light that I perceived that never before (and that after many confessions and absolutions) had I believed it with my whole heart. . . . Jesus has cancelled the handwriting that was against us. Lift up our hearts! (Collected Letters of C. S. Lewis, 3:151-52)
Five years later, in another letter, Lewis related the experience more fully to a woman who had freshly discovered the awe-full reality of Christ's incarnation.
Almost exactly the same thing that happened to you about the Incarnation happened to me a few years ago about the Forgiveness of Sins. Like you, I had assented to the doctrine years earlier and would have said I believed it. Then, one blessed day, it suddenly became real to me and made what I had previously called 'belief' look absolutely unreal. It is a wonderful thing. But not, on inferior matters, so very uncommon. We all in one sense 'believe' we are mortal: but until one's forties does one really believe one is going to die? On the edge of a cliff can't one believe, and yet not really believe, that there's no danger? But certainly this real belief in the truths of our religion is a great gift from God. When in Hebrews 'faith' is defined as 'the substance of things hoped for,' I would translate 'substance' as 'substantialness' or 'solidity' or (almost) 'palpableness.' (ibid., 751)