Because saving faith does not itself produce the righteousness (grace, justification, forgiveness of sins) by which the sinner is saved, but merely accepts the merits that have been secured for the world by Christ’s obedience and are offered to all men in the Gospel, our dogmaticians have called it a passive act (actus passivus) or a passive instrument (instrumentum passivum). J. A. Osiander thus writes: Receptio alicuius rei non est actio, sed passio. And Dannhauer: Fides patitur sibi benefieri.
These expressions are Scriptural; for in his conversion man does not himself contribute anything, but only receives everything as a free gift of God. However, saving faith may be called an actus passivus, or an instrumentum passivum, also in view of the fact that it is engendered and preserved not by man himself, but solely through the gracious operation of the Holy Ghost, ; . In other words, the penitent sinner does not believe in Christ by his own reason or strength, but trusts in Him for salvation only because the Holy Ghost has called him by the Gospel, enlightened him with His gifts, and sanctified him. The Augsburg Confession says : “Although nature is able in a manner to do the outward work, . . . yet it cannot produce the inward motions, such as the fear of God, trust in God, chastity, patience, etc.” In this sense faith is called a passive act or a passive instrument.
However, these expressions must not be understood as if saving faith were not in itself essentially an act of the believer (actus apprehendendi) . To deny the activity of faith in this sense would mean to deny the essence of faith; for saving faith is by its very nature an act of trusting, or confiding, by which the believer appropriates to himself the grace offered to him in the Gospel. So Holy Scripture itself describes faith when it speaks of it as “receiving the atonement,” , or “receiving Christ,” .
To express the fact that faith is essentially an act of trusting in the Gospel, our dogmaticians have said that saving faith is fides actualis, or active confidence. Moreover, they teach on the basis of Scripture (; ; ; ; ; ; ) that to believe means “to desire grace,” “to seek Christ,” “to stretch out the hand toward Christ,” “to embrace Christ,” “to come to Christ,” “to approach Christ,” “to run toward Christ,” “to cleave to Christ,” “to hold to Christ,” “to join oneself to Christ,” etc.
All who deny that saving faith is essentially an act of apprehending (actus apprehendendi) and regard it merely as an “inactive quality” (otiosa qualitas) or as a mere “ability to believe” (potentia credendi) deny faith altogether; for a faith that does not trust in Christ is not faith at all, but a mere fancy. In fact, if faith is said to save sinners inasmuch as it is a good quality, then salvation is based upon good works, since in that case faith saves as a human virtue.
Luther very strenuously affirmed that the act of apprehending divine grace is the outstanding characteristic of that true faith which is wrought by the Holy Ghost, whereas a mere faith of the head (historic faith) or a mere knowledge of the facts of salvation does not lay hold of the merits of Christ offered to the sinner in the Gospel. Saving faith, then, is always an act of the believer,, though it is an act wrought by the Holy Ghost. Luther: “Fides est habere Verbum in corde et non dubitare de Verbo”