Temporary believers and other unregenerate people may deceive themselves in vain with false hopes and fleshly presumptions that they have God’s favor and salvation, but their hope will perish (Job 8:13-14; Mt 7:22-23). Yet those who truly believe in the Lord Jesus and love him sincerely, endeavoring to walk in all good conscience before him, may be certainly assured in this life that they are in a state of grace. They may rejoice in the hope of the glory of God (1Jn 2:3; 3:14, 18-19, 21, 24; 5:13), and this hope will never make them ashamed (Ro 5:2, 5).
This certainty is not merely an inconclusive or likely persuasion based on a fallible hope. It is an infallible assurance of faith (Heb 6:11, 19) founded on the blood and righteousness of Christ revealed in the Gospel (Heb 6:17-18). It is also built on the inward evidence of those graces of the Spirit about which promises are made (2Pe 1:4-5, 10-11). It is further based on the testimony of the Spirit of adoption, witnessing with our spirits that we are the children of God (Ro 8:15-16). As a fruit of this assurance, our hearts are kept both humble and holy (1Jn 3:1-3).
This infallible assurance is not such an essential part of faith that it is always fully experienced alongside faith, but true believers may wait a long time and struggle with many difficulties before obtaining it (Isa 50:10; Ps 77:1-12; 88). Yet with the enabling of the Spirit to know the things freely given to them by God, they may attain this assurance using ordinary means appropriately without any extraordinary revelation (1Jn 4:13; Heb 6:11-12). Therefore, it is the duty of all to be as diligent as possible to make their calling and election sure. In this way their hearts may be enlarged in peace and joy in the Holy Spirit, in love and thankfulness to God, and in strength and cheerfulness in the duties of obedience. These effects are the natural fruits of this assurance (Ro 5:1-2, 5; 14:27; Ps 119:32). Thus, it does not at all encourage believers to be negligent (Ro 6:1-2; Tit 2:11-12, 14).
True believers may in various ways have the assurance of their salvation shaken, decreased, or temporarily lost. This may happen because they neglect to preserve it (SS 5:2-3, 6) or fall into some specific sin that wounds their conscience and grieves the Spirit (Ps 51:8, 12, 14). It may happen through some unexpected or forceful temptation (Ps 31:22; 77:7-8; 116:11) or when God withdraws the light of his face and allows even those who fear him to walk in darkness and to have no light (Ps 30:7). Yet they are never completely lacking the seed of God (1Jn 3:9), the life of faith (Lk 22:32), love of Christ and the brethren, sincerity of heart, or conscience concerning their duty. Out of these graces, through the work of the Spirit, this assurance may at the proper time be revived (Ps 42:5, 11). In the meantime, they are kept from utter despair through them (La 3:26-31).