Only in a world of sincere men is unity possible;—and there, in the long-run, it is as good as certain.
For observe one thing, a thing too often left out of view, or rather altogether lost sight of in this controversy: That it is not necessary a man should himself have discovered the truth he is to believe in, and never so sincerely to believe in.
 Thomas Carlyle, On Heroes, Hero-Worship, and The Heroic in History (1841). copy citation

Context

“has no power of sympathy even with things,—or he would believe them and not hearsays. No sympathy even with things; how much less with his fellow-men! He cannot unite with men; he is an anarchic man. Only in a world of sincere men is unity possible;—and there, in the long-run, it is as good as certain. For observe one thing, a thing too often left out of view, or rather altogether lost sight of in this controversy: That it is not necessary a man should himself have discovered the truth he is to believe in, and never so sincerely to believe in. A Great Man, we said, was always sincere, as the first condition of him. But a man need not be great in order to be sincere; that is not the necessity of Nature and all Time, but only of certain corrupt unfortunate epochs of Time.” source