Here is a good illustration from old Dr. Lyman Beecher, which is going the rounds of the press:—
"Young Gentlemen," said the Doctor, pausing in the midst of a lecture on Divine Decrees, and raising his spectacles over his forehead,—a way he had when some extemporaneous thought struck him,—"Theology is a mighty deep. It has its calms and its storms, its joys and its dangers; and many weak souls, and some strong ones, are wrecked, because they venture too far without taking proper bearings. I go out myself, sometimes, but I try to be careful. I walk along the shore, and pick out some sturdy old stump of a doctrine, which has stood there firmly for thousands of years, and never been pulled out. I make fast to that, and so, when I miss my footing, I haul on the line. I don't know where I am, but I know where that stump is. I settled that point before I started."