I’ll start right out by saying that I think this is an unfortunate term and not a Scriptural concept. I know that many preachers get a lot of mileage out of the term, but it has some problems.
First, since the term “sin nature” is not a Scriptural term, we have difficulty defining it correctly. No major Bible version uses the term. The NIV is the only major translation that uses the term “sinful nature” and it does so to translate the term “flesh” when used in a sense other than the physical body. The only other Bible version that does this to the extent of the NIV is the New Living Bible. Using “sinful nature” for “the flesh” is an interpretation and not a true translation. According to most theologians it is an error of interpretation. The Greek word is always the same, always simply “sarx”, which means flesh.
There are two primary ways in which we use the word “nature” in ordinary speech. We may speak of that which defines something as being its nature. My nature, then, would be that which makes me to be me. It is the thing I hold in common with anyone else like me. It is separate from the things of my life. For example: I could say that I have a home in the USA. That is not part of my nature. If my home was in India, I would still be me. I have two ears, but if I only had one or if I had none, I would still be me. I speak English, am under 6 feet tall, drive a Ford, like chocolate, am married, and wear glasses. Yet, if any or all of these things changed, I would still be me. My nature is something more fundamental, more integral to the definition of what I am.
I am human, dependent on outside provision, bound by the laws of physics. If any of these were not true, I would be something quite different from what I am. I would no longer have the same nature. This is the kind of thing that is meant by the term when it is used in the realm of theology or philosophy. When we speak of the nature of God, we refer to His characteristics or attributes that are essential to who or what He is. Scripture tells us several things. He is Spirit; He is Love; He is almighty, all-knowing, and ever present; He is eternal. If He were not these things, His nature would be different.
There is another way in which we use the term “nature” that may cause some of the confusion. We say things like, “It was his nature to arrive promptly at 6:00 AM.” We may be talking about a person, but we may also be talking about a horse, a dog or even a familiar gust of wind. In this usage, a better term might be “way” or “habit.” It is not a true sense of the term “nature”, but it is common use.
So, what do we mean when we say that we have a “sin nature?” Do we mean that we habitually sin? Or do we mean that our core, our essence, is sinful? Is there any difference between those who have come to Christ and those who have not? Do believers still have a sinful nature?