The body politic is like a big group of people that make decisions together. When a country has a body politic, it means that all the people who live there have the right to vote and choose their leaders through a democratic process. Just like how you might vote for your class president, the body politic votes for things like who will be the president of their country or what laws they want to have.
The body politic is also used to describe the physical body of a ruler. It's like a metaphorical way of saying that the ruler is the head of the body and all the people are different parts that work together to make the body function. So just like how your brain tells your body what to do, the ruler makes decisions for the country and everyone else follows them.
Overall, the body politic is a way of describing how people come together to make important decisions about their country, and how they all work together to keep it running smoothly.