1. The grace of faith, whereby the elect are enabled to believe to the saving of their souls (Heb. 10:39), is the work of the Spirit of Christ in their hearts (2 Cor. 4:13; Eph. 1:17–19; 2:8), and is ordinarily wrought by the ministry of the Word (Rom. 10:14, 17), by which also, and by the administration of the sacraments, and prayer, it is increased and strengthened (1 Pet. 2:2; Acts 20:32; Rom. 4:11; Luke 17:5; Rom. 1:16–17).
The ordinary course of events is this: the Word is preached, and God uses that Word to transform a sinner’s heart by the agency of the Holy Spirit. As a result of this transformed heart, the elect are enabled to believe to the saving of their souls. If they could have repented and believed with their old heart, they didn’t need a new one. But once this transformation is complete, the Word and resultant faith do not disappear. The Word, along with baptism, the Lord’s Supper, and prayer, works to increase and strengthen the faith of the believer. Please note that the grace that is being strengthened by the sacraments here is saving grace. The work following conversion has much in common with the work of conversion.
2. By this faith, a Christian believeth to be true whatsoever is revealed in the Word, for the authority of God Himself speaking therein (John 4:42; 1 Thess. 2:13; 1 John 5:10; Acts 24:14); and acteth differently upon that which each particular passage thereof containeth; yielding obedience to the commands (Rom. 16:26), trembling at the threatenings (Isa. 66:2), and embracing the promises of God for this life, and that which is to come (Heb. 11:13; 1 Tim. 4:8). But the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life, by virtue of the covenant of grace (John 1:12; Acts 16:31; Gal. 2:20; Acts 15:11).
The faith which is worked in us by the Spirit causes us to believe as true anything revealed in the Bible. This is done because the quickened individual sees the authority of God Himself in the Scriptures. But although God is always the one speaking, He does not always say the same thing. In some passages, He threatens, causing the faithful to tremble. He commands, causing the faithful to seek the way of obedience. In other places, He promises, causing the faithful to trust in the promises for eternal life, as well as the present life. But the center place is occupied with the Word which brings us to accept receive and rest upon Christ alone for our justification, sanctification, and eternal life. All this is done under the terms of the covenant of grace, set forth in the Scriptures.
And note that the “principal acts” of saving faith include trusting Christ alone for sanctification. Trusting Christ alone for justification and eternal life seem to us like “converting” motions of faith. But the Westminster divines were very clear that one of the central things done by saving faith is to trust Christ for sanctification. Put another way, if it is not trusting Christ alone for sanctification, then it is not saving faith.
3. This faith is different in degrees, weak or strong (Heb. 5:13–14; Rom. 4:19–20; Matt. 6:30; 8:10); may be often and many ways assailed, and weakened, but gets the victory (Luke 22:31–32; Eph. 6:16; 1 John 5:4–5): growing up in many to the attainment of a full assurance, through Christ (Heb. 6:11–12; 10:22; Col. 2:2), who is both the author and finisher of our faith (Heb. 12:2).
This faith is not to be understood as a standard unit of divine manufacture. Rather, it is like an organic plant. If it is alive, it will grow up into full assurance of faith at some point, whether in this life or the life to come. But while in this life, the faith in one man may look quite different than the faith in another man. Faith admits of degrees, and may be weak or strong, great or small, triumphant or cautious. But regardless, genuine faith gets the victory.