The concluding sentence restates the ultimate authority of the action. Furthermore, it implicitly claims apostolic continuation of the specific method of transmitting the Holy Ghost. Moroni gives this to us not for historical reasons, but as a model.
Thus was it done, thus should it be done. In fact, the modern practice follows this format, but without the necessity of repeating precise words (though that will be part of the sacramental liturgy discussed later.)
Textual: This is the end of a chapter in the 1830 edition.