Summary: There is a belief that the old sinful nature is eradicated the moment a person becomes a Born-Again Christian and that they now have only one wholly sanctified nature.
There is a belief that the old sinful nature is eradicated the moment a person becomes a Born-Again Christian and that they now have only one wholly sanctified nature. It is believed that one way to view "nature" is to understand it as a "capacity" within the Born-Again Christian, which means that the 'old man' is interpreted as the former way of life because they have two competing capacities within them - the old capacity to sin and the new capacity for godliness so they can resist sinning and put it to death, once and for all, but God did not create a dualistic, bipolar and schizophrenic Christian with two natures; He recreated just one totally new person in righteousness and holiness.
Indeed, the Bible does not use the explicit words "sin nature" (See Rom 7:14-25, 8:3; 2 Pet 2:18). However, the Bible also does not use the word "trinity" or "rapture" either, but the concepts are still implicitly presented throughout Scripture.
The Bible teaches that every human being has an earthly nature that wants to sin as a result of the Fall when Adam and Eve willingly chose not to trust God and believe His Word (Col 3:5). The earthly nature is commonly referred to as the 'flesh' (Heb' basar') in the Old Testament and is used to denote the actual physical body of all living things, and particularly humanity as a whole (Gen 2:21, 6:12-13; 41:2; Ps 16:9, 102:5).
The Hebrew word 'basar' is also used is used interchangeably with "soul" and "body," and about human relationships, emotions and responses (Lev 13:8; Judges 9:2; Isa 40:6; Ps 63:1; 84:2), as well as in reference to mutability and weakness, and also infers the idea of softness (2 Chron 32:8; Isa 31:3; Ezek 11:19; Ps 78:39).
In the Hebrew thought, the understanding of a human being is that there is nothing merely physical because humans do not have flesh, but are flesh. God created human beings (i.e., flesh) as good, just as all other parts of His creation (Job 10:8-12; Ps 119:73; Isa 45:12). God desired that human flesh be fully dependent upon Him for everything (Gen 2:7; 6:3; Isa 31:3). However, because of the Fall, the flesh was exposed to the endless assault of sin and is now frail and transitory (Gen 6:3,5,13; Ps 78:39; Isa 40:6). All of the New Testament uses of the word 'flesh' are built upon the foundation of Old Testament understanding.
The Death of the Flesh
Every human being in this mortal life begins to die from the ravaging effects of sin's sickness and disease on human flesh from the moment they are born. No one is immune from death (unless they are 'raptured' out of this world)! However, at the very moment, a person becomes spiritually Born-Again; they are given eternal life because they were forgiven of all their sins!
Within the science of Physics, there is a branch known as the Laws of Thermodynamics. The second law is known as entropy, which is an empirical biological reality and scientific absolute. Entropy is why things deteriorate, and the body breaks down as it ages. People go bald, hair turns gray, glasses are needed to see, skin wrinkles, bones get brittle, teeth decay, and organs ultimately fail. Everything dies because cells stop dividing, and organs stop working impairing normal functioning, which is the definition of disease. No matter how much 'faith' a person conjures up, they can't escape it. Natural death of the flesh can't be cured.
A person puts on spiritual immortality when they become Born-Again. Death is the ultimate sickness. However, the mortality of this life that ends in death is swallowed up by eternal life when a person dies in Christ (1 Cor 15:53-55).
The sin nature of humankind is not born-again when a person receives Jesus as their personal Lord and Savior through repentant humility. Everyone on this planet sins before God. Sin still reigns in the body of the Born-Again Christian, who is a 'saved' sinner, but still a sinner, none-the-less. That can be seen in the Apostle Paul's statement about the battle of the flesh:
"So I find it to be a law that when I want to do right, evil lies close at hand. For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin." (Rom 7:21-25 ESV)
The biblical truth is that every human being has a mortal and perishable body that is subject to weaknesses and is being torn down and destroyed by sin (1 Cor 15:42-43; 2 Cor 4:16-5:1) which is the reason why the Apostle Paul told that Galatians that "it was because of a bodily ailment that I preached the gospel to you at first, and though my condition was a trial to you, you did not scorn or despise me, but received me as an angel of God, as Christ Jesus" (Gal 4:13–15).