Where the sanction of the Christian world, or the force of habit and custom, or the apparent insignificance of what we do, makes us think little of the sin, it has a terrible power to deceive the professing Christian. And through this deceitfulness of sin, be it worldliness, or unlovingness, or pride, or want of integrity, hearts are hardened, and become incapable of hearing the voice of God.

Andrew Murray, The Holiest of All, p. 138