For they have made ready their heart like an oven - He gives the reason old their bursting out into open mischief; it was ever stored up within. They “made ready,” (literally, “brought near”) “their heart.” Their heart was ever brought near to sin, even while the occasion was removed at a distance from it. “The “oven” is their heart; the fuel, their corrupt affections, and inclinations, and evil concupiscence, with which it is filled; “their baker,” their own evil will and imagination, which stirs up whatever is evil in them.” The prophet then pictures how, while they seem for a while to rest from sin, it is but “while they lie in wait;” still, all the while, they made and kept their hearts ready, full of fire for sin and passion; any breathing-time from actual sin was no real rest; the heart was still all on fire; “in the morning,” right early, as soon as the occasion came, it burst forth.
The same truth is seen where the tempter is without. Such, whether Satan or his agents, having lodged the evil thought or desire in the soul, often feign themselves asleep, as it were, “letting the fire and the fuel which they had inserted, work together,” that so the fire pent-in might kindle more thoroughly and fatally, and, the heart being filled and penetrated with it, might burst out of itself, as soon as the occasion should come.