We must try to keep the mind in tranquility. For just as the eye which constantly shifts its gaze, now turning to the right or to the left, now incessantly peering up and down, cannot see distinctly what lies before it, but the sight must be fixed firmly on the object in view if one would make his vision of it clear, so too man's mind when distracted by his countless worldly cares cannot focus itself distinctly on the truth.

vol. 1, p. 9 - Letters