In the third sentence of the first paragraph, the author mentions society's ability to "execute its own mandates" primarily to

The author mentions society's ability to "execute its own mandates" primarily to show that the citizens of a society must act on free will unless they harm others. It is then the government should interfere to provide protection to the society.

Explanation:

Adapted from 'On Liberty' by John Stuart Mill

John Stuart Mill stated: "Society can and does execute its own mandates; and if it issues wrong mandates instead of right, or any mandates at all in things with which it ought not to meddle, it practices a social tyranny more formidable than many kinds of political oppression, since, though not usually upheld by such extreme penalties, it leaves fewer means of escape, penetrating much more deeply into the details of life, and enslaving the soul itself."

The author mentions society's ability to "execute its own mandates" primarily to show that the citizens of a society must act on free will unless they harm others. It is then the government should interfere to provide protection to the society.