Jamieson, Fausset and Brown on Isaiah 5:18

18. Third Woe--against obstinate perseverance in sin, as if they wished to provoke divine judgments.

iniquity--guilt, incurring punishment [Maurer].

cords, &c.--cart-rope--Rabbins say, "An evil inclination is at first like a fine hair-string, but the finishing like a cart-rope." The antithesis is between the slender cords of sophistry, like the spider's web (Is 59:5; Job 8:14), with which one sin draws on another, until they at last bind themselves with great guilt as with a cart-rope. They strain every nerve in sin.

vanity--wickedness.

sin--substantive, not a verb: they draw on themselves "sin" and its penalty recklessly.