On Anger, Book 2, Section 31 — In Plain English

Seneca — The Senator

It's wrong to harm your country. So it's also wrong to harm any of your fellow citizens, because each citizen is part of the country. If the whole is sacred, then the parts must be sacred too. Therefore it's also wrong to harm any human being. Every person is your fellow citizen in the larger community of humanity. What if your hands decided to hurt your feet? Or your eyes decided to hurt your hands? All our body parts work together because the whole body benefits when each part stays healthy. In the same way, people should protect each other, because we were born to live together. But society can only work if it protects and cares for all its members.

Seneca — The Senator Original

It is a crime to injure one's country: so it is, therefore, to injure any of our countrymen, for he is a part of our country; if the whole be sacred, the parts must be sacred too. Therefore it is also a crime to injure any man: for he is your fellow-citizen in a larger state. What, if the hands were to wish to hurt the feet? or the eyes to hurt the hands? As all the limbs act in unison, because it is the interest of the whole body to keep each one of them safe, so men should spare one another, because they are born for society. The bond of society, however, cannot exist unless it guards and loves all its members.