To one who studies the career of Fray Isidro Félix de Espinosa, the strangest fact of all lies in finding that so little was known of him for a century and a half after his death. When Don José Beristain y Souza finally issued his Biblioteca Hispano Americana Setentrional in 1819, all his knowledge of Fray Isidro was summed up in these few lines:
Espinosa (Fr. Isidro Félix)—Native of the city of Querétaro, of the Province of S. Peter and S. Paul of Michoacán, of the Order of S. Francis. Preacher, missionary apostolic, guardian, and chronicler of the College de Propaganda Fide of the Holy Cross of Querétaro; censor of books for the Tribunal of the Inquisition. He was as tireless in his preaching of the Divine Word as he was in perpetuating the apostolic deeds of his brethren; and due to that fact was worthy of being termed “the Julius Caesar of the Gospel in New Spain.” For, like that Roman, he fought by day (though better battles) and wrote by night.