The absolution is truly certain and everlasting, although you may not believe it, just as the sun truly shines and beams in the heavens and is the true sun, although you may not see it or you may crawl into a cellar where you cannot see it. But that would be your fault, not the sun's. God nonetheless considers it the true sun, which He has created to be a light to the world...Just so,...absolution is entirely certain. If then, you do not believe the absolution, it is not its fault but yours.
(Dr. Martin Luther - from What Luther Says - para 8 - page 6).