Petrus van Mastricht

Nor does he become the author of sin by his providence, because that lawlessness is nothing except a defect of operation, of which there cannot exist an author or efficient cause, but only a deficient cause, for which reason alone, the author of sin, insofar as it is such, is the creature, by its transgressing of the law.

God certainly does not in either case effect or infuse blindness or hardness into the sinner (cf. James 1:13–14), yet neither does he only not take away blindness and hardness, by not circumcising the heart (Jer. 6:10, 26; Acts 7:51), or by not conferring spiritual light to the mind, or softness and malleability to the heart (Matt. 13:14–15; Isa. 6:9–10), but in addition: (1) on account of preceding sins, in a just and holy way, he takes away or diminishes the remnants of wisdom and moral goodness that a sinner has, and also augments and aggravates his original blindness and hardness.

Yet we are able to reconcile them easily enough, if we distinguish within sin its material element, namely, the habit or act that is the substrate of the wickedness, with which, inasmuch as it is physically good, God is not able not to concur as the efficient cause, without casting aside his own independence (Acts 17:28; Rom. 11:36), and its formal element, lawlessness (1 John 3:4), through which the act or habit is sin, whose author he cannot be, because the one set above all law cannot transgress the law.

God by his influence is indeed the principal cause of the act itself, but man is the sole cause of the sin itself, which is in that act. … Nor can even one theologian be shown who has said that God is the author of lawlessness, or of sin insofar as it is sin.

The Reformed on the contrary state that all concupiscence, which certainly inclines toward evil, is sin, insofar as (1) all such concupiscence is against the law (Rom. 7:7) and thus is lawlessness, in which sin fully consists (1 John 3:4).

The Reformed on the contrary state that all the acts of concupiscence, even the primary-first, are sins, because the contrary opinion is: (1) contrary to the express words of the apostle (Rom. 7:7); (2) contrary to the express demand of the law (Ex. 20:17); (3) contrary to the force and strictness of the law, which under the penalty of an eternal curse demands the most exact obedience (Matt. 22:37; Deut. 27:26; Gal. 3:10), and therefore condemns all concupiscence.

Accordingly, it is not valid to say: (1) it begets sin, therefore it is not sin. For a man, because he begets a man, does not cease to be a man; indeed, as we have said, it is sin by the very fact that it begets sin.