Rom 2:29 – But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Colossians 2:11 – In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
If you changed from a human being to a horse, you would know and so would everyone else. According to II Cor 5:17, the Christian becomes a new creature in Christ when saved. The flesh is attached to the soul and one has a dead spirit before salvation. When a person is born again, the soul is separated from the flesh, the spirit is quickened or made to live, and a new creature is made. All that cannot happen to someone and things not drastically change in their life.
You probably would not think that circumcision and eternal security go hand in hand, but they do. Circumcision is a cutting away of flesh. When we are saved, the Holy Ghost literally cuts our flesh away from soul according to Col. 2:11. To me that teaches eternally security of the believer more than anything. Because the soul is no longer attached to the flesh, when the flesh sins, it is no longer accounted to the soul. The soul is cleansed by the blood of Christ. The born again believer should become very aware of his three parts (body, soul and spirit) the moment he is saved. He becomes schizophrenic. His flesh wants to go one way and his soul another.
In addition to the soul being separated from the flesh, Romans talks about the heart also being separated from the flesh when someone is saved. The heart is deceitful and desperately wicked, however, when someone believes on Christ like Abraham did, according to Romans his heart set aside for God’s use. He gets a new and clean heart. It is no longer totally depraved. He now serves God from a new perspective, especially if he was religious before he got saved. He no longer serves God out of the letter of the law, but rather God puts praise in his mouth. There is a newness that goes along with salvation.
So if you are feeling a little schizophrenic today, that is a good thing as a Christian. The apparatus is functioning properly. Your flesh is fighting against the spirit and the spirit against the flesh. That’s wonderful! There needs to be a battle of the two, or the flesh is likely going to win. Be not overcome of evil, but overcome evil with good (Rom 12:21).