12. Take heed, (or See,) brethren, lest there be at any time in any of you a wicked heart of unbelief, etc. I have preferred to retain literally what the Apostle states, rather than to give a paraphrase as to the wicked or depraved heart of unbelief, by which he intimates that unbelief would be connected with depravity or wickedness, if after having received the knowledge of Christ they departed from his faith. For he addressed them who had been imbued with the elements of Christianity; hence he immediately added, By departing; for the sin of defection is accompanied with perfidy. (62)
(62) The word connected with “heart” is ἐν τῶ, which properly means diseased and hence corrupted, depraved, wicked. Depraved or wicked would perhaps be the best rendering of it here. “Unbelief” is a genitive used for an adjective or a participle, — “a wicked unbelieving heart.” It is unbelieving owing to its wickedness or depravity. Grotius says, that there are two kinds of unbelief, — The first the rejection of the truth when first offered, — and the second the renouncing of it after having once professed it. The latter is the more heinous sin.
“The departing,” etc.; ἐν τῶ is rendered “by” by Macknight: it is considered by Grotius to be for εἰς τὸ, which word makes the meaning more evident, “so as to depart,” etc. — Ed.