Love is the expression of one's values, the greatest reward you can earn for the moral qualities you have achieved in your character and person, the emotional price paid by one man for the joy he receives from the virtues of another.
-Ayn Rand, Atlas Shrugged
In the Nicomachean Ethics, Aristotle wrote that the greatest good for human beings was to be found in their capabilities for reason, and that the most choiceworthy life for a human being was one dedicated to the enhancement of our understanding. We need not follow Aristotle in thinking that study is “the activity of (the) divine element” (1177b25, translation by Terence Irwin) to agree with him that the most excellent and praiseworthy traits of human life have to do with the life of the mind. Not only have those rational traits given our species the capability of bringing the challenge of Genesis 1:27 to completion, but it has also enabled each individual person agency, the capability to reflect back upon their lives, and to decide who they want to be.
Although surely encumbered by a wounded nature, human beings have, by their rational nature, a world of possibilities in front of them. Through reflection and erudition, they can expand those possibilities, and learn to differentiate the virtuous from that which is not. If rationality means anything, it means that the rational agent can do those two things.
As for the former, in her lecture “Apollo and Dionysus,” Ayn Rand, ever the Apollonian, noted that it was “man's reason that brought him to the stars.” By virtue of their rationality, human beings can understand chains of concatenation within the world, and manipulate those causal nexus, as what occurs within a Saturn V rocket upon ignition, in order to better their position in the world.
As for the latter, St. Thomas Aquinas wrote in Book III, Chapter 3 of his Summa Contra Gentiles (translation by Ralph McInerny) that the rational agent “acts for the sake of an end, determining itself to the end” and later that the rational agent “determines an end for itself only under the formality of the good...” Rationality was thus the part of the human being that enables her to be able to discern the good in the world, and to strive after it.
It is here, in these two aspects that we find what is really commendable in human beings across the world: their ability, as ends in and of themselves (to throw Herr Kant into the mix), to make the world, both external and internal, according to their own decisions. Relating to the external world, our reason has enabled us to raise skyscrapers, and, even more amazingly when we actually ponder about it, to devise ways to feed around seven billion human beings who now call Earth home. Relating to the internal world, our reason has enabled us to envision our own virtue, to have a moral vision of what we ought to be, and to be able to give that vision chase with all of our human passion. This is what each person should take pride in, what deserves admiration from others, and what deserve to be the foundation of a truly human identity.