Thomas Aquinas 
Summa Theologica (Part 2.1) 

This brilliant synthesis of Christian thought has had a decisive and permanent impact on religion since the 13nth century and has become substantially the official teaching of the Catholic Church. The
Summa Theologica, as the title indicates, is a summing up of all that can be known about God and humanity’s relations with God. It is divided into three parts dealing with god, man, and the God-man respectively. It consists of 38 tracts, 631 questions, about 3000 articles, 10, 000 objections and their answers. Essential reading for all who are interested in core Christian thought.