As to the Persons they are distinct; but as to the substance they are one.
39. How are the three Divine Persons distinct from one another?
By this: that the Father is begotten of no one, nor proceeds from any one; the Son is begotten of the Father; and the Holy Ghost proceeds from the Father and the Son.
40. But if the Son is begotten of the Father, and the Holy Ghost proceeds from both, why, then, is none of the Divine Persons older than the others?
Because the Son is begotten from all eternity, and the Holy Ghost also proceeds from all eternity.
41. Why is the Father called the 'first,' the Son the 'second,' and the Holy Ghost the 'third' Person?
They are so called, not to show any superiority, but the order in which the one proceeds from the other from all eternity.
42. What works are principally attributed to each of the three Divine Persons?
1. To the Father are attributed the works of omnipotence, and particularly the Creation; 2. To the Son, the works of wisdom, and particularly the Redemption; and 3. To the Holy Ghost, the works of love, and particularly Sanctification; although these works are common to all three Persons.
The works of Omnipotence and Creation are particularly attributed to the Father, because He is the principle to which the two other Persons owe their eternal origin. The works of Wisdom to the Son, because the Father begets the Son by the knowledge of Himself, wherefore the Son is also called the essential 'Image,' the eternal 'Word' of the Father.
The works of Love are attributed to the Holy Ghost, because He proceeds from the mutual love of the Father and of the Son.
43. What do we call the mystery of one God in three Persons?
We call it the mystery of the Most Blessed Trinity.