Belloc's Perspective on Islam and Catholicism

Belloc cited the many beliefs and theological principles which Islam shares with Catholicism. Where Islam decisively diverges from Catholicism (and Christianity in general) is the denial of the Incarnation and all the sacramental life of the Church that followed from it.

The Great Heresies and the Protestant Reformation

In The Great Heresies Belloc grouped the Protestant Reformation together with Islam as one of the major heresies threatening the Church Universal.