Since saving faith is the believer’s trust in the perfect righteousness which Christ has secured for all men by His vicarious satisfaction and which therefore exists even before a person believes, it is clear that a believer is in full possession of divine pardon, life, and salvation from the very moment in which he puts His trust in Christ; for in that very moment all the merits of Christ’s suffering and death are imputed to him, Acts 16, 31. For this reason the believer is also certain of his salvation; for saving faith is in its very nature the truest and greatest certainty. If papists and Romanizing Protestants deny that the believer may be sure of his salvation, it is because they teach that salvation, in part at least, depends on the believer’s good works, in other words, because they intermingle justification with sanctification. It is evident that all who reject the sola gratia and make salvation depend on man’s character, righteousness, and good works must deny also the certainty of salvation. Work-righteousness always produces doubt and uncertainty, while personal trust in the vicarious atonement of Christ and His objective justification always effects a most joyous assurance of salvation in the believer’s heart. From this follows the rule that, if a believer wishes to be sure of his salvation, he must unflinchingly adhere to the gracious promises of the Gospel. As soon as he turns away from them, he will be lost in a sea of doubt.
The certainty of salvation, which is produced through the Gospel, is not natural (fides humana), but supernatural and spiritual (fides divina), since it is wrought in the heart of the believer by the Holy Ghost through the means of grace. By nature all men seek salvation by works. Hence the certainty of salvation which the unregenerate claim to possess is based upon their compliance with the divine Law, Luke 18, 11. Such certainty, however, must be condemned as sinful presumption, since all who would be justified by the Law are under the curse, Gal. 3, 10. True certainty, on the other hand, which trusts divine grace without works, is the gift of the Holy Ghost, 1 Cor. 2, 4. 5.