Chapter 2 — Part I — On Faith and the Creed
Section 72. Q. What were the particular occasions for assembling the first and second œcumenical Councils, at which the Creed was defined? A. The first was held for the confirmation of the true doctrine respecting the Son of God, against the error of Arius, who thought unworthily of the Son of God; the second, for the confirmation of the true doctrine respecting the Holy Ghost, against Macedonius, who thought unworthily of the Holy Ghost.