Every spark of fire is fire, and will burn; so is every thing of the law of sin, the last, the least of it, -- it is enmity, it will poison, it will burn. … Mortification abates of its force, but doth not change its nature. Grace changeth the nature of man, but nothing can change the nature of sin. Whatever effect be wrought upon it, there is no effect wrought in it, but that it is enmity still, sin still.

Accordingly, we hold that there is always sin in the saints until they are freed from their mortal frame, because depraved concupiscence resides in their flesh, and is at variance with rectitude.

The corruption of nature, during this life, does remain in those that are regenerated (Rom. 7:18, 23; Eccl. 7:20; 1 John 1:8); and although it be through Christ pardoned and mortified, yet both itself, and the first motions thereof, are truly and properly sin (Rom. 7:23–25; Gal. 5:17).

That which lusts against the spirit, and by lusting tempts, and in tempting entices and draws the heart to sin, is for nature sin itself: but concupiscence in the regenerate lusts against the spirit, Gal. 5. 17. … And therefore it is sin properly: such as the fruit is, such is the tree.

That concupiscence does not condemn the regenerate, comes to pass by an accident, which is the grace of God, which does not impute it to the faithful. This, however, does not occur in this way, as though concupiscence were no sin; for other sins in like manner do not condemn the regenerate, not because they are no sins, but because they have obtained the pardon of them through Christ.