Because the chief aim of sacred doctrine is to teach the knowledge of God, not only as He is in Himself, but also as He is the beginning of things and their last end, and especially of rational creatures, as is clear from what has been already said, therefore, in our endeavor to expound this science, we shall treat: (1) Of God; (2) Of the rational creature's advance towards God; (3) Of Christ, Who as man, is our way to God.
In treating of God there will be a threefold division, for we shall consider: (1) Whatever concerns the Divine Essence; (2) Whatever concerns the distinctions of Persons; (3) Whatever concerns the procession of creatures from Him.
Concerning the Divine Essence, we must consider: (1) Whether God exists?
(2) The manner of His existence, or, rather, what is NOT the manner of His existence; (3) Whatever concerns His operations -- namely, His knowledge, will, power.
Concerning the first, there are three points of inquiry:
A Whether the proposition "God exists" is self-evident?
A Whether it is demonstrable?
A Whether God exists?