“Faith alone saves, but faith that is alone is not the genuine article. It’s not saving faith.”
This is clear in Scripture, and Reformers taught such. Sola Fide means that God-given faith appropriates justification by imputed righteousness (Rm. 3:9-5:1), but it is IMPOSSIBLE to Biblically believe on the Lord Jesus Christ without effectually confessing Him as such, as enabled. Faith, like love, causes responses corresponding to the desires and will of it’s object. What you really believe will be manifest in what you do. But the key distinction is that it is not by any merit of our works, which must includes even the heart assent of faith or “sinners prayer,” that we are justified by, but by imputed righteousness, appropriated by God-given faith. Thus it cannot be said that souls “by their very works sake.. have merited eternal life” (Trent), if that is to mean that by any merit of works themselves one is justified.
Paul (against the Jews) in Romans 4 and elsewhere deals with the very issue of upon what basis sinful man is justified, and states that God justifies a man by faith without requiring works as regards a means of merit. But elsewhere makes it clear such faith is a confessional one. James (against “easy believers”) specifically deals with what manner of faith is saving, and requires works as a condition of salvation. What i believe both are saying is that God only imputes righteousness in response to a confessional faith, which begins in the heart, but which will (if at all possible) be manifested outwardly, and seals such faith as salvific, and without such it is considered incomplete. And which confession God also enables. But again, it is not be any merit of any confession that one is saved, but by imputed righteousness true faith appropriates.
James is not contrary to Paul in this who attests, “That if thou shalt CONFESS with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth CONFESSION is made unto salvation” (Rom 10:10). If one does believe in the heart, such a faith, if real, will constrain confession. “We having the same spirit of faith, according as it is written, I believed, and therefore have I spoken; we also believe, and therefore speak” (2 Cor 4:13). The Lord Himself stated, “Whosoever therefore shall confess me before men, him will I confess also before my Father which is in heaven” (Mat 10:32). And the writer of Hebrews declares that Jesus “became the author of eternal salvation unto all them that obey him” (Heb 5:9).
And so we see that true faith and confession are inseparable, and that the only kind of faith that saves is one that will manifest heart faith by outward confession. But what constitutes a confession? It is a manifestation of response, which begins at the heart, the outward confession of which Paul states here is by the mouth. But confession is surely not limited to the mouth, but can be any faith (in Christ as Lord and Savior) motivated action. As regards bodily action besides the mouth, the primary formal manifestation is volitional baptism (Mark 16:16), which for some can be a “sinner’s prayer” in body language (Acts 2:38). This is not adding works to salvation, any more than the mental assent of faith is. In another instance, previously lost (Acts 11:14) Cornelius and household believed on the Lord Jesus and received the Holy Spirit just as the apostles did, before they spoke or were baptized (Acts 10:43-47; 15:7-9; Eph. 1:13).
Selah!