no mortal is doomed to be an insincere man. Whole ages, what we call ages of Faith, are original; all men in them, or the most of men in them, sincere.
 Thomas Carlyle, On Heroes, Hero-Worship, and The Heroic in History (1841). copy citation

Context

“it is sincerity. The believing man is the original man; whatsoever he believes, he believes it for himself, not for another. Every son of Adam can become a sincere man, an original man, in this sense; no mortal is doomed to be an insincere man. Whole ages, what we call ages of Faith, are original; all men in them, or the most of men in them, sincere. These are the great and fruitful ages: every worker, in all spheres, is a worker not on semblance but on substance; every work issues in a result: the general sum of such work is great; for all of it, as genuine, tends towards one goal;” source