I prefer this more modern formulation because the self-evidence of the proposition is more easily seen. And that statement is a self-evident truth, because its denial is unaffirmable. Both denials are non-sensical. They involve human being simultaneously affirming and denying his existence as a human being. They inviolate a human being violating the law of non-contradiction which governs both thought and reality.
Human beings actualize their human nature in a particular way.
As rhetorical shorthand, I might say that detailed obligation is the obligation to become truly and fully human. This shortform is helpful because human beings and human nature are commensurate universals. They are defined in terms of each other. Human nature is really nothing more than the set of potentials the actualization of which makes me truly and fully human. The pragmatic test of whether a person has successfully actualized his potential is whether he is truly and fully human, or something less.