The sin nature is that principal in man that makes him rebellious against God because of a natural inclination to his ways, and the desire to naturally choose to do our own thing. Sin entered into the world by the fact of Adam’s fall and all are born in sin, because of Adam’s transgression. A good example of the existence of sin nature is that no one has to teach a child to lie or be selfish; rather we go to great lengths to teach children to tell the truth and also love other people.
Christians have two natures at work in their being; one is the old sin nature, and the other is the Divine Nature controlled by the Spirit. When Rabecca had conceived, it was said unto her; “The elder shall serve the younger” (Romans 9:12). In the spiritual analysis, this means that the sin nature, which is the oldest in the believer because one has a sin nature at birth, will serve the divine nature, which is younger and comes into the believer at conversion.
In his psalm David said that “Behold, I was shaped in iniquity; and in sin did my mother conceived me” (Psalm 51:5). This indicates that all are born in sin, as a result of Adam’s fall in the Garden of Eden. This did not exclude anyone irrespective that all did not in essence commit transgression as did Adam, they were still sinners.
Thank God because Adam was the fountainhead of all sin and death, while Jesus Christ is the Fountainhead of all redemption and life. Therefore as by the offence of one, judgment came upon all men to condemnation; even so by the Righteousness of one (Jesus Christ) the free gift came upon all men unto the justification of life” (Romans 5:18). This is received by simply believing in what Jesus Christ has already accomplished freely for all of us at the cross, which is the only answer for sin. While there is medicine for different types of diseases, there is no medicine in the hospitals or pharmacies that can deal with the sin nature apart from having faith in Jesus Christ and the cross.
The good news is that while the two natures are constantly in conflict, it is not the sin nature that will ultimately control the Christian. It is part of the sanctification process to die to the sin nature. The bible tells us that we are no longer controlled by the sin nature if we believe in Jesus Christ, and the spirit of God lives in us.