Well, I’ve read a lot of the answers. There seems to be some confusion.
do we believe that removing sin doesn’t change our nature,
Correct. Removing sin is a personal thing. Nature is not. Let me give you an example.
The Blessed Trinity shares one divine nature. That nature is such that there is only one, it is eternal, omnipotent and omniscient.
We also share one human nature with the rest of humanity. That one nature is shared by many persons. And it is such that every individual human is confined to a space in time, not eternal, not omniscient, not omnipotent and imperfect.
Unless you want to say that one human whose sins are forgiven makes humanity better, in general, human nature is not affected when one individual is forgiven by God and He removes our sin, washing it away in the washing of regeneration, which is Baptism. An individual soul is renewed and washed clean of all sin.
but that through sanctification our natures would be changed?
Sanctification is also a personal thing. Washing of sin, or removal of sin, is a very important part of sanctification. Every time our sins are removed and we are washed of sins, we are sanctified. But we are also sanctified every time that we do a good deed, every time that we pray, and every time that we move closer to God.
But our nature is not affected. Only our soul.
I’ve never heard that our natures would be changed.
The early church used the metaphor of an iron in the fire. The process of sanctification is like putting an iron rod in the fire. The iron rod will begin to glow and may become almost indistinguishable from the fire. But it is not the fire. The same for human nature, we may become perfect as our Father in heaven, but we will never be God. We will only look like Him:
1 John 3:2 Beloved, we are God’s children now; what we shall be has not yet been revealed. We do know that when it is revealed[a] we shall be like him, for we shall see him as he is.