Body politic is a phrase referring to a collective body of people belonging to a country, state, or society. In other words, a collection of politically organized people. It is sometimes used to describe a group as a single unit, unified in purpose or action. Usually it is used with the article the, as in the body politic.
This phrase is appositive, which means the modifier comes after the noun it relates to. Politic is describing body, not the other way around.