Justifying faith applies the word to practice; it includes the lesser species as the perfect includes the imperfect; assurance of pardon is not its primary act

Now justifying faith is that by which not only the theoretical intellect is illumined, so that it certainly believes the things taught by the word of God, but also the practical mind of man is so affected that it refers those things to practice and applies them to itself. For the truly faithful person so believes, for example, the promises of the Gospel concerning remission of sins and eternal happiness and glory, that he firmly and effectually judges his highest good and blessedness — to which he must aspire with all his strength — to be placed in them; so he gives faith to the mysteries of our redemption that he plainly thinks consolation and peace of conscience are to be sought for himself in them; finally he so considers the divine commandments that he certainly resolves within himself that life is to be lived according to them.

From which it can be clear that justifying faith is so diverse from historical and temporary faith that it includes all their virtue; and is so distinguished from them as the perfect from the imperfect — or by that distinction by which a higher grade differs from a lower. For justifying faith stands to the remaining species of faith as the rational soul stands to the sensitive and vegetative; whose force and faculties — life, sense, and motion — it eminently embraces, and adds the grade of reason. For so also justifying faith makes us believe all things taught by the word of God, which historical faith performs. And if God should promise something special and call someone to work a miracle, then it also supplies the force of miraculous faith; nor does the one who already believes the word of God as he ought, if a special promise is directed to him, need a new habit in order to give assent to it. Hence it is that the Apostle, commending the force and efficacy of saving faith, attributes to it various miraculous works which holy men once wrought, or which were done for their sake: saying that by faith the fathers crossed the Red Sea, and by faith the walls of Jericho fell, and by faith some stopped the mouths of lions and quenched the power of fire (Hebrews 11). But above the remaining species of faith, justifying faith has this: that it more brightly irradiates the theoretical mind, more fully imbues the practical, penetrates more deeply, and begets a sharper sense of truth and a firmer assent in our souls than historical or temporary faith. Then also whatever it has drawn from the word of God it refers to action and to the ordering of life; and in the way we have said, it applies it to itself.

Which application is indeed to be understood rightly, and in the sense already set out. Not, however, as though the proper act of justifying faith, by which it is discerned from the other species of faith, consisted in this: that someone should bring himself to think that his sins are remitted, and that he is a child of God predestined to life, and will certainly be a partaker of salvation. For this persuasion, if it is legitimate, necessarily presupposes faith and arises from it; and therefore cannot be its primary act. For since remission of sins and eternal life are promised in the Gospel to no one absolutely, but under the condition of faith and repentance: in order that we may be certain of the grace of God and of our salvation, it is necessary that it first be clear to us concerning our faith and repentance. From which it is manifest that that certainty of faith is a consequent, not faith itself; or if someone wishes it to belong to faith, at least that it is not its primary act.