He served as an Army chaplain in the Arauco War during the government of Don Francisco Laso de la Vega and, in 1640, was ordained a priest in Santiago.

In 1650, Governor Antonio de Acuña Cabrera tasked him to conduct a journey to the Pehuenche tribes east of Villarica and later to Lake Nahuelhuapi.

The second part deals with the history of the Kingdom from the arrival of Diego de Almagro until the General Rising of 1655.

Diego de Rosales Historia documents a series of events such as the Dutch expedition to Valdivia.

It was a series of biographies of the main missionaries of the order, combined with the descriptions of their personalities with tales of miracles, appearances and all sorts of wonders common in the minds and documents of the time.