Throughout the month of June, in honor of the Unity of the Three Divine Persons, there will be excerpts from the Roman Catechism of the Council of Trent provided for your reflection.
The Doctrine Of The Trinity
In the one Substance of the Divinity the Father is the First Person, who with His only begotten Son, and the Holy Ghost, is one God and one Lord, not in the singularity of one Person, but in the trinity of one Substance. These Three Persons, since it would be impiety to assert that they are unlike or unequal in any thing, are understood to be distinct only in their respective properties. For the Father is unbegotten, the Son begotten of the Father, and the Holy Ghost proceeds from both. Thus we acknowledge the Essence and the Substance of the Three Persons to be the same in such wise that we believe that in confessing the true and eternal God we are piously and religiously to adore distinction in the Persons, unity in the Essence, and equality in the Trinity.
Hence, when we say that the Father is the First Person, we are not to be understood to mean that in the Trinity there is anything first or last, greater or less. Let none of the faithful be guilty of such impiety, for the Christian religion proclaims the same eternity, the same majesty of glory in the Three Persons. But since the Father is the Beginning without a beginning, we truly and unhesitatingly affirm that He is the First Person, and as He is distinct from the Others by His peculiar relation of paternity, so of Him alone is it true that He begot the Son from eternity. For when in the Creed we pronounce together the words God and Father, it means that He was always both God and Father.