It seems like we are just speaking entirely different languages on this point. You are very concerned with the idea of ‘being born again’ which indeed is crucial, but we just don’t view it in the same context that you do.
For us, the new birth does not concern swapping of natures. Human beings are human beings. The human nature governs human acts. This concerns natural things only.
The new birth or the laver of regeneration concerns supernatural things. We also agree that humans need the divine life operating within their immortal souls, but we do not view this supernatural life as something in tension with natural realities.
That is why I spoke earlier of dualism. From what I’ve read, it seems that the Evangelical regards natural things as incompatible with supernatural things. The natural is believed to be evil or bad and the supernatural good.
We firmly reject such notions. It is not a question of natural vs. supernatural, but whether they are in proper order, harmony, integration. Supernatural is not at odds with the natural, rather it must govern the natural.
Sin then is not the cause of human nature per se (though the weakness of the human condition is what allows sinfulness) but the result of a serious disorder in nature. In other words, the human person is disordered because the person does not operate as he ought to.
We understand faith to be the summit of the human person. Faith is the key which unlocks every spiritual and supernatural reality. Thus, without faith, the higher things will not guide the lower things as they ought to.
That is the sin of Adam. Adam had no knowledge of good or evil, and he was not required to make a rational decision about the tree. Instead, God asked Adam to have faith in Him and to hearken to His voice. Rather than do this, Adam listened to his instincts and subordinated faith to reason (or irreason) and impulses.
We believe every human being suffers from this condition of Adam. That is the inheritability of original sin.
The process of being born again involves a rebirth of divine life within man. By faith, we receive the spirit and act according to the spirit. The natural then is subordinated to the spirit. We do the works of God instead of dead works of the flesh.
You possess a human nature before being born again. Do you lose this human nature when you are born again? If the answer is no, then I do not understand this talk of changing natures. We don’t discard human nature, we place it under the divine life by faith through grace. What we are as humans is incorporated within a higher, more beautiful, spiritual vocation.
Finally, when it comes to the nature of Christ, it seems that you are trying to have it both ways. We believe that Jesus Christ possesses a human nature, will, and soul. These three aspects of the Christ are perfect, without defect, and in perfect harmony with the divine nature. Ultimately, this is what illustrates the point I am trying to make. Jesus’ human will interacts in perfect accord with His divine will. His human nature is perfectly immaculate and blameless. His Sacred Heart is consummated in radical charity. We refer to these truths as the hypostatic union. Jesus is Man and God, true, whole, blameless, without tension or discord.
To be born again, is to be remade in the image of Christ. The image of Christ is what I speak of above. Through the action of grace, our will must be united to His will, our nature brought into perfect accord with His nature, our heart and soul made clean.