WLC Q.72: What is justifying faith?
Justifying faith is a saving grace, (Heb. 10:39) wrought in the heart of a sinner by the Spirit (2 Cor. 4:13, Eph. 1:17–19) and word of God, (Rom. 10:14–17) whereby he, being convinced of his sin and misery, and of the disability in himself and all other creatures to recover him out of his lost condition, (Acts 2:37, Acts 16:30, John 16:8–9, Rom. 5:6, Eph. 2:1, Acts 4:12) not only assenteth to the truth of the promise of the gospel, (Eph. 1:13) but received and rested upon Christ and his righteousness, therein held forth, for pardon of sin, (John 1:12, Acts 16:31, Acts 10:43) and for the accepting and accounting of his person righteous in the sight of God for salvation. (Phil. 3:9, Acts 15:11)
WCF 11.2.
Faith, thus receiving and resting on Christ and His righteousness, is the alone instrument of justification: (John 1:12, Rom. 3:28, Rom. 5:1) yet is it not alone in the person justified, but is ever accompanied with all other saving graces, and is no dead faith, but worketh by love. (James 2:17, 22, 26, Gal. 5:6)