Chapter 2 — Part I: The Creed — Introduction on Faith and the Creed
Section 8. For, as has been observed by our predecessors in the faith, who have treated this subject with great piety and accuracy, the Creed seems to be divided into three principal parts: one describing the First Person of the Divine Nature, and the stupendous work of the creation; another, the Second Person, and the mystery of man's redemption; a third, the Third Person, the head and source of our sanctification; the whole being expressed in various and most appropriate propositions. These propositions are called Articles, from a comparison frequently used by the Fathers; for as the members of the body are divided by joints (articuli), so in this profession of faith, whatever is to be believed distinctly and separately from anything else is rightly and suitably called an Article.