What is most profitable for everyone is what fits their own nature. My nature is to be rational in all I do. As a good citizen, I should be kind and helpful to my fellow members of society. As Antoninus, my city is Rome. As a human being, my city is the whole world. Therefore, what is good for these communities is the only thing that is good for me.
Now that unto every one is most profitable, which is according to his own constitution and nature. And my nature is, to be rational in all my actions and as a good, and natural member of a city and commonwealth, towards my fellow members ever to be sociably and kindly disposed and affected. My city and country as I am Antoninus, is Rome; as a man, the whole world. Those things therefore that are expedient and profitable to those cities, are the only things that are good and expedient for me.