The materials gathered from Philosophy, Tradition, and Scripture were the fruit of analysis; the final synthesis had yet to be accomplished. This was the scope of the 'Summa Theologica,' a work which, though it was not completed, is the greatest production of Thomas Aquinas. In the prologue he says:-- "Since the teacher of Catholic truth should instruct not only those who are advanced, but also those who are beginning, it is our purpose in this work to treat subjects pertaining to the Christian religion in a manner adapted to the instruction of beginners. For we have considered that young students encounter various obstacles in the writings of different authors: partly because of the multiplication of useless questions, articles, and arguments; partly because the essentials of knowledge are dealt with, not in scientific order, but according as the explanation of books required or an occasion for disputing offered; partly because the frequent repetition of the same things begets weariness and confusion in the hearer's mind. Endeavoring, therefore, to avoid these defects and others of a like nature, we shall try, with confidence in the Divine assistance, to treat of sacred science briefly and clearly, so far as the subject-matter will allow." The work intended for novices in theology, and so unpretentiously opened, is then portioned out in these words:-- "Whereas, the chief aim of this science is to impart a knowledge of God, not only as existing in Himself, but also as the origin and end of all things, and especially of rational creatures, we therefore shall treat first of God; second, of the rational creature's tendency toward God; third, of Christ, who as man is the way whereby we approach unto God. Concerning God, we shall consider (1) those things which pertain to the Divine Essence; (2) those which regard the distinction of persons; (3) those which concern the origin of creatures from Him. As to the Divine Essence we shall inquire (1) whether God exists; (2) what is, or rather what is not, the manner of His existence; (3) how He acts through His knowledge, will, and power. Under the first heading we shall ask whether God's existence is self-evident, whether it can be demonstrated, and whether God does exist."