The purpose of the author is to inform. With this wording the author is presenting the information to allow the reader a better understanding of his own perspective or point of view towards the situation taking place.
The quote doesnt include persuasive language to evoke a feeling, change the reader's mind nor is the author instructing the reader or someone what or how to do something.
The second best choice would be to entertain, as this biographical work is meant to inform and like most literature is also meant to entertain, but the most important relevant element is to inform and provide perspective of the situation he was facing.
