WLC Q.80: Can true believers be infallibly assured that they are in the estate of grace, and that they shall persevere therein unto salvation?
Such as truly believe in Christ, and endeavour to walk in all good conscience before him, (1 John 2:3) may, without extraordinary revelation, by faith grounded upon the truth of God’s promises, and by the Spirit enabling them to discern in themselves those graces to which the promises of life are made, (1 Cor. 2:12, 1 John 3:14,18–19,21,24, 1 John 4:13,16, Heb. 6:11–12) and bearing witness with their spirits that they are the children of God, (Rom. 8:16) be infallibly assured that they are in the estate of grace, and shall persevere therein unto salvation. (1 John 5:13)
WCF 18.1.
Although hypocrites and other unregenerate men may vainly deceive themselves with false hopes and carnal presumptions of being in the favour of God, and estate of salvation (Job 8:13–14, Micah 3:11, Deut. 29:19, John 8:41) (which hope of theirs shall perish): (Matt. 7:22–23) yet such as truly believe in the Lord Jesus, and love Him in sincerity, endeavouring to walk in all good conscience before Him, may, in this life, be certainly assured that they are in the state of grace, (1 John 2:3, 1 John 3:14,18–19,21,24, 1 John 5:13) and may rejoice in the hope of the glory of God, which hope shall never make them ashamed. (Rom. 5:2,5)