…and thou shalt not be at all concerned, but shalt be able to pass over duties, praying, hearing, reading, and thy heart not in the least affected. Sin will grow a light thing to thee; thou wilt pass it by as a thing of nought; this it will grow to. And what will be the end of such a condition?
Can a sadder thing befall thee? Is it not enough to make any heart to tremble, to think of being brought into that estate wherein he should have slight thoughts of sin? Slight thoughts of grace, of mercy, of the blood of Christ, of the law, heaven, and hell, come all in at the same season.
Take heed, this is what thy lust is working towards,—the hardening of the heart, searing of the conscience, blinding of the mind, stupefying of the affections, and deceiving of the whole soul.
John Owen. Mortification of Sin in Believers.
