Doubt is but another element of faith.
For, were it not good that evil things should also exist, the omnipotent God would almost certainly not allow evil to be, since beyond doubt it is just as easy for Him not to allow what He does not will, as for Him to do what He will.
Nobody should ever doubt that in the washing of rebirth (Titus 3:5) absolutely all sins, from the least to the greatest, are altogether forgiven.
If a parricide is more wicked than anyone who commits homicide-because he kills not merely a man but a near relative-without doubt worse still is he who kills himself, because there is none nearer to a man than himself.
Everyone who observes himself doubting observes a truth, and about that which he observes he is certain; therefore he is certain about a truth. Everyone therefore who doubts whether truth exists has in himself a truth on which not to doubt.... Hence one who can doubt at all ought not to doubt the existence of truth.