John Calvin on Doubt

The whole, then, comes to this: As soon as the minutest particle of faith is instilled into our minds, we begin to behold the face of God placid, serene, and propitious; far off, indeed, but still so distinctly as to assure us that there is no delusion in it. In proportion to the progress we afterwards make, (and the progress ought to be uninterrupted), we obtain a nearer and surer view, the very continuance making it more familiar to us. Thus we see that a mind illumined with the knowledge of God is at first involved in much ignorance, - ignorance, however, which is gradually removed. Still this partial ignorance or obscure discernment does not prevent that clear knowledge of the divine favor which holds the first and principal part in faith. For as one shut up in a prison, where from a narrow opening he receives the rays of the sun indirectly and in a manner divided, though deprived of a full view of the sun, has no doubt of the source from which the light comes, and is benefited by it; so believers, while bound with the fetters of an earthly body, though surrounded on all sides with much obscurity, are so far illumined by any slender light which beams upon them and displays the divine mercy as to feel secure.

- John Calvin, The Institutes of Christian Religion