Faith in Jesus Christ as Saviour is not the same as faith in Jesus Christ as my Saviour, nor are these the same as believing that I am saved. The latter is assurance of salvation.
Saving faith says: “I believe in Jesus Christ for the salvation of my soul.”
Assurance of salvation says: “I believe that I have believed in Jesus Christ for the salvation of my soul.” Assurance is a particular exercise of faith, but it has a different object.
We are justified by faith in Jesus Christ Rom 5:1.
We come to the knowledge of this justification also by faith, faith in Jesus’ teaching on the subject. This is shown by Rom 5:2, a less well-known text than Rom 5:1. Jesus taught that the publican was justified Lk 18:14, but neither we nor the publican would know it unless Jesus taught it. If Scripture did not teach justification by faith, one would not believe it Rom 10:17. We do not need to go up to heaven to find out Rom 10:6, because the answer is in the Scripture Rom 10:8-11.
Faith in Jesus Christ as God’s appointed Saviour comes through hearing the Gospel Rom 10:17 and being persuaded that Jesus Christ is the Son of God Act 8:37 and Jn 5:24-25 and thus He can be trusted in all that He says and does.
Faith in Jesus Christ as my Saviour comes through understanding and believing that Jesus Christ offers Himself in the Gospel to be the Saviour of all those who hear the Gospel Rev 22:17, thus He is offering me this unspeakable privilege, and through this understanding one believes in Christ as one’s personal Saviour and commits one’s soul to Him for salvation, as He freely offers Himself as such in the Gospel 2Tim 1:12.
James asserts that some of those who claim to have faith in Jesus Christ are mistaken Jam 2:17. So Paul exhorts us to examine ourselves whether we be in the faith 2Cor 13:5.
Different objects of assurance
Similarly with assurance – one can be sure about different things. One may be sure about things concerning Christ, one may be sure about things concerning oneself, and also about others.
Peter was sure that Jesus was the Christ, the Son of God Jn 6:69 and Jesus assured him that this conviction or assurance came from His Father in heaven Mat 16:16-17. This was not the direct testimony of the Holy Spirit to Peter’s spirit, but the teaching of Jesus informing and assuring him of something that he did not know. It is recorded in Scripture for our benefit and for our use to examine ourselves.
The disciples were sure that Jesus knew all things and had come from God Jn 16:30.
Some people are sure that they are saved and will go to heaven; and Jesus says that some of them are deceived Mat 7:21-23. Some have this assurance through an experience and others through self-examination by the Word of God. Scripture exhorts us to make our calling and election sure 2Pe 1:10. There is a difference between making it sure to ourselves and making it sure to others. Confusion reigns by a failure to notice these distinctions.
Some people are sure that they are saved but not sure about getting to heaven; this is Arminian or Semi-Pelagian theology, which teaches that a saved person may fall from grace. Yet such a person claims to believe Jesus Christ is his Saviour, but what sort of salvation is this if one can lose it? What sort of assurance is this? For Arminians, assurance of salvation is not the same as assurance of getting to heaven, which is hardly assurance at all.
Assurance about ourselves is not the same as assurance about Christ.