Complex sentence: He is now considered to be the author of the "Compendium theologiae" or "Compendium theologicae veritatis", which, on account of its scope and style, as well as its practical arrangement, was for 400 years used as a text-book.
Split into simpler sentences: He is now considered to be the author of the "Compendium theologiae" or "Compendium theologicae veritatis". On account of its scope and style, as well as its practical arrangement, was for 400 years used as a text-book.