Albert Barnes Commentary Job 8:15

"He shall lean upon his house, but it shall not stand: He shall hold fast thereby, but it shall not endure." — Job 8:15 (ASV)

He shall lean upon his house - This is an allusion to the web or house of the spider. The hope of the hypocrite is called the house which he has built for himself: his home, his refuge, his support. But it will fail him. In times of trial he will trust to it for support, and it will be found to be as frail as the web of the spider. How little the light and slender thread that a spider spins would avail someone for support in time of danger! So frail and unsubstantial will be the hope of the hypocrite! It is impossible to conceive of any image that would more strongly describe the utter vanity of the hopes of the wicked.

A similar comparison occurs in the Quran, Surah 28:40: “They who assume any other patrons to themselves besides God, are like the spider building his house; for the house of the spider is most feeble.”

He shall hold it fast - Or, he will lay hold of it to sustain himself, denoting the eagerness with which the hypocrite seizes upon his hope. The image is still taken from the spider and is an instance of careful observation of the habits of that insect. The idea is that the spider, when a high wind or a tempest blows, seizes upon its slender web to sustain itself. But it is insufficient. The wind sweeps all away. So the tempest of calamity sweeps away the hypocrite, though he grasps at his hope and would seek security in that, just as a spider does in the light and tenuous thread that it has spun.