When I was on chemo-therapy, I took the liberty to change some medications that I was on without notifying my doctor. The change in medicines had an adverse effect. I was plunged into depression and despair. All I could see was blackness and darkness. Everything seemed hopeless. I was even questioning the existence of God. If He did exist I had no assurance that I knew Him.
During that time I knew that the only way I could be saved was if Christ did everything in my salvation. I could not even come up with the faith. Perhaps that is the purest my faith has ever been.