In the controversies on faith the question has been propounded whether a Christian may be sure of possessing true faith. The question has been emphatically denied by Romanists and Romanizing Protestants, while Holy Scripture very strenuously affirms it, 2 Tim. 1, 12; 4, 7.
It is true, a believer may not always be conscious of his faith. Saving faith (fides directa, fides actualis) need not always be conscious faith (fides reflexa), or faith which is perceived by the believer. (Fides reflexa et discursiva, qua homo renatus credit et sentit se credere.) Thus Christian adults, while asleep or engrossed with their daily occupation, indeed possess direct faith, which truly apprehends the grace of God in Christ Jesus, yet not reflex and discursive faith. That is to say, they meditate neither on their act of faith nor on their state of faith. For the time being faith with all that it implies has passed out of their direct consciousness. They may even be in a condition of coma, not being able to reflect on spiritual things at all; or they may be in a state of trial (in statu tentationis), when they believe themselves to be without faith because they have lost the sense, or feeling, of faith (sensus fidei). In all such cases saving faith truly exists, though the believer is not conscious of it. Even in baptized infants, faith is not a mere potentiality to believe (potentia credendi) or an inactive quality (otiosus habitus), but fides actualis, or actual trust in, and active apprehension of, divine grace (actus apprehendendi), as Christ directly testifies (Matt. 18, 6: οἷ μικροὶ οἷ πιστεύοντες εἰς ἐμέ).
However, the doctrine regarding reflex faith must not be abused in the interest of carnal security and indiffercntism; for it is God’s will that all believers should be sure of their state of faith and grace, Rom. 5, 1. 2. If Christians entertain doubts concerning their faith, such doubts should be removed. This necessitates the preaching of the Law in order to show that unbelief and doubt are sinful and displeasing to God, John 8, 46; Matt. 14, 31. But above all the preaching of the Gospel is necessary, Rom. 5, 20; 8, 15—17, which alone works certainty of faith, John 8, 31. 32, and dispels all doubts.
It is well to remind the doubting, fearing Christian also of the fact that even the desire to be saved through Jesus Christ is already actual, or direct, faith; for such a desire is never found in the natural, unregenerate heart, 1 Cor. 2,14, but is the gift of the Holy Spirit, Eph. 1, 19; Rom. 8, 23. The Formula of Concord rightly says (Thor. Decl., II, 14): “To all godly Christians who feel and experience in their hearts a small spark or longing for divine grace (scintillula aliqua et desiderium gratiae divinae) and eternal salvation this precious passage Phil. 2, 13 is very comforting; for they know that God has kindled in their hearts this beginning of true godliness and that He will further strengthen and help them in their great weakness to persevere in true faith unto the end.” (Cf. Matt. 17, 20: 1 ᾿Εὰν ἔχητε πίστιν ὡς κόκκον σινάπεως.)
Because the assurance which a believer has concerning His state of grace (certitudo gratiae) is not found in man’s heart by nature, but is engendered in him by the Holy Spirit, it is rightly said that such certainty rests upon the testimony of the Holy Ghost (testimonium Spiritus Sancti). The testimony of the Holy Spirit is both internal (testimonium Spiritus Sancti internum) and external (testimonium Spiritus Sancti externum). The internal, or direct, witness of the Holy Spirit is nothing else than faith, which assures the believer that he is a child of God, consoles and strengthens him in all adversity and temptation, and preserves him in the hope of eternal life, Rom. 8, 15. 16; 1 John 5, 10; Phil. 1, 6. The internal testimony of the Holy Spirit is therefore not something that exists without faith or by the side of faith, but it is faith itself, 1 John 5, 10. Cp. the Apology (Trigl., p. 154, § 113, German text): “But faith, properly so called (proprie dicta), is when my heart and the Holy Ghost in the heart says: The promise of God is true and certain. Of this faith Scripture speaks.”
The external testimony of the Holy Spirit consists in this, that God through the means of grace works in the believer manifest fruits of faith, such as love for God and His Word, John 8, 47; 1 Thess. 1, 3—6; 2 Thess. 2, 13—15, and love for the neighbor, 1 John 3, 14, which bear witness to his state of grace. Gal. 5, 22—24. This external witness of the Holy Ghost, which occurs only in true believers, must be distinguished from the carnal trust which the unregenerate put in their external “good works,” which carnal trust in their “dead good works” proves convincingly that they are self-righteous and therefore not children of God, Luke 18, 10—14.
Every true believer in Christ therefore is sure of his state of grace and salvation; for the Holy Spirit, who through the Gospel has engendered faith in him, assures him by that very faith that he is a child of God and an heir of eternal life, Rom. 8, 15—17.