What is the purpose of the enclosed seeds in a fruit found on a flowering plant?

The primary purpose of the seed in a fruit is reproduction.

A seed is a matured, fertilized ovule of a flowering plant and it contains an embryo  by which a new plant can grow.

 Plants are able to perpetuate themselves mainly through sexual means through seeds which when they germinate become seedlings. Seedlings facilitate the propagation of plants.

Seeds also serve as diaspores or dispersal units themselves . Many seeds have adaptations such as fine hairs, parachutes, hooks and water repellent surfaces which enhance their dispesal.