That’s a great question. We do have a new nature. We have the nature of God. With Him, we are one spirit. However, we still live in this fallen mortal body.
Our new nature in Christ is a big topic with life-changing revelations to be discovered. 1st Year Charis Bible College has courses such as Life Foundations and Galatians that will help you uncover these revelations. Click the link at the bottom of this article to learn more about Charis programs and enrolment.
So to the question of ‘why do we sin?
Well, the body didn’t get transformed at salvation. Only your spirit got transformed. And so we still deal with something called the flesh. Let me read to you out of Galatians. I’m going to read from Galatians 5:16 and 17:
I say then: Walk in the Spirit, and you shall not fulfil the lust of the flesh. For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish.
So Paul is making it very clear here that though you be born again and you can now walk in the Spirit which you couldn’t do before you were born again. Nevertheless, there is still a flesh war going on. Now in the Spirit, we are equipped to win that war.
We do not have to succumb to the lusts of the flesh. We can walk in the Spirit. We can choose the things of the Spirit. And so that’s why, though we have a new nature, you still have an old body, in that sense, you still have your flesh to deal with. It still has its appetites, its lusts, its desires.
Before we were born again, all we had to fight that would be the willpower of our minds. The law of the mind, so to speak. You never win that battle. You cannot beat flesh with flesh. But by the Spirit of God, we can. We can choose love, joy, peace, patience, goodness, kindness, self-control. We can choose to walk in the Spirit. And when we walk in the Spirit, we don’t fulfill the lusts of the flesh.