Jamieson, Fausset and Brown on Job 8:15

15. he shall hold it fast--implying his eager grasp, when the storm of trial comes: as the spider "holds fast" by its web; but with this difference: the light spider is sustained by that on which it rests; the godless is not by the thin web on which he rests. The expression, "Hold fast," properly applies to the spider holding his web, but is transferred to the man. Hypocrisy, like the spider's web, is fine-spun, flimsy, and woven out of its own inventions, as the spider's web out of its own bowels. An Arab proverb says, "Time destroys the well-built house, as well as the spider's web."