Repentance is not proof of our salvation.  It is evidence of our salvation. Proof is for mathematics and logic. When people talk about the proof of something they’re talking about establishing something as a fact, something that is absolutely true. But, when someone repents of sin, we cannot ‘prove’ that such a person is saved based on his repentance. We cannot know the person’s heart in order to determine if it is true or false repentance.   After all, there is such a thing as false repentance.

2 Corinthians 7:10, “For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation, but the sorrow of the world produces death.”

Undoubtedly, someone who is truly born again (John 3:3-8; 2 Cor. 5:17) will display certain fruit of the Spirit (Gal. 5:22-23).  Repentance is one of the things that God grants to us (2 Tim. 2:25) and will manifest in those who are saved.  But, as I previously stated, we cannot look into the heart of a person to see whether not he or she is saved.  But, we can make spiritual judgments regarding their behavior (1 Cor. 2:15).  So, if someone says he is a Christian but does not turn from his sin, that is evidence he is not really saved. Repentance is one of the pieces of evidence of salvation, but not the only one. Other evidences are a desire to follow God, fellowship with other Christians (Heb. 10:25), manifesting-love (1 Cor. 13:1-8), being a disciple of Jesus (Matt. 28:19-20), etc.

Repentance of the false believers

There are many people who repent of their sins but are never Christians. Mormons and Jehovah’s Witnesses, for example, can repent of their sins based on what they see in the Bible, but this is not proof of their salvation. After all, both such groups deny the true God, the true Christ, and the true gospel.  They aren’t saved.

Conclusion

So we can conclude that repentance is a work of God granted to the true Christian (2 Tim. 2:25), as is faith (Phil. 1:29; John 6:28-29), and is one of the evidences of regeneration. But, we cannot look into the hearts of people to discern whether they are truly saved or not. We can only look at their works.  So, repentance from sin is not proof a person is saved.  It is evident that a person is saved – as long as they are not also denying the true God, true Christ, and true gospel.