Four Hundred Texts on Love (Fourth Century) 6

13.  Whether or not a nature endowed with intelligence and intellect is to exist eternally depends on the will of the Creator whose every creation is good; but whether such a nature is good or bad depends on its own will.

First, we are contingent beings. We have no natural immortality. Thus our existence is not part of our nature in the sense that it is something we control. When Christ broke the chains of death he did so for all humanity. However, our acts for good or ill do depend on our will. In that sense we form part of our nature.