what is the purpose if this text?

Do you mean the purpose of the text as a whole? I think the theme of Home resonates the most. While all these characters enjoy trekking out into the world, it is equally important that they can enjoy the stability of home once they return. The theme manifests in different ways for each character. Rat and Badger are more set in their domesticity, and prefer to stay close to home, while Mole and Toad want to see as much of the world as they can. However, Mole and Toad are also glad to have somewhere to call their own. It is no accident that the novel ends with a triumphant return to Toad Hall, since it closes the story by reaffirming the power of home.