Job 31:12

For this is an heinous crime; and the chiefest iniquity. For it is a fire that consumeth to destruction, and that rooteth out all increase. There is this difference between 'sin' and 'crime,' that all crime is sin, but not all sin is crime. And in this life there are numbers without crime, but no one can be without sins. And hence the holy preacher, when he was describing a man worthy of the grace of the priesthood, never said, 'if any be without sin,' but if any be without crime.

So the text continues, "it (adultery) is a fire, which devours even to consuming," because it cheats a man of his whole patrimony, as has been said, "and eradicates all seed," when it makes the succession of his sons uncertain, and so Sirach says, "Every …

For it is a fire that consumeth to destruction,....

For it is a fire - Nothing is so destructive of domestic peace. Where jealousy exists, unmixed misery dwells; and the adulterer and fornicator waste their substance on the unlawful objects of their impure affections.

For it is a fire that consumeth to destruction - This may mean that such an offence would be a crime that would provoke God to send destruction, like a consuming fire upon the offender (Rosenmuller and Noyes), or more likely it is designed to be descriptive of the nature of the sin itself. According to this, the meaning is, that indulgence in this sin tends wholly to ruin and destroy a man. It is like a consuming fire, which sweeps away everything before it. It is destructive to the body, the morals, the soul. Accordingly, it may be remarked that there is no one vice which pours such desolation through the soul as licentiousness. See Rush on the Diseases of the Mind. It corrupts and taints all the fountains of morals, and utterly annihilates all purity of the heart. An intelligent gentleman, and a careful observer of the state of things in society, once remarked to me, that on coming to the city of Philadelphia, it was his fortune to be in the same boarding-house with a number of young men, nearly all of whom were known to him to be of licentious habits. He has lived to watch their course of life; and he remarked, that there was not one of them who did not ultimately show that he was essentially corrupt and unprincipled in every department of morals. There is not any one propensity of man that spreads such a withering influence over the soul as this; and, however it may be accounted for, it is certain that indulgence in this vice is a certain evidence that the whole soul is corrupt, and that no reliance is to be placed on the man’s virtue in any respect, or in reference to any relation of life. And would root out all mine increase - By its desolating effects on my heart and life. The meaning is, that it would utterly ruin him; compare Luk 15:13, Luk 15:30. How many a wretched sensualist can bear testimony to the truth of this statement! […]