Lust in the bud; that is, the first risings of lust, even before the consent of the will to them; the first openings of particular lusts, sometimes not regarded nor noticed, and so neither approved nor disapproved; and sometimes checked in their very rising, Rom. 7:15. But however it be, they are sins here forbidden, though the Papists will not allow them to be so

We again regard it as sin whenever man is influenced in any degree by any desire contrary to the law of God; nay, we maintain that the very pravity which begets in us such desires is sin.

If that law demands perfect conformity to the image of God, then these impulses of evil are clearly sinful. … The Protestant doctrine which pronounces these impulsive acts to be of the nature of sin is confirmed by the consciousness of the believer. He recognizes as evil in their own nature the first risings of malice, envy, pride, or cupidity.

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.

The inmost thoughts of the heart, and the first motions of concupiscence therein, though not consented unto, much less actually accomplished in the outward deeds of sin, and all the occasions leading unto them, are directly forbidden in the law.