Understanding the Trinity: Three Persons One God

"In order to be able to describe what was revealed concerning the Incarnation, it is necessary to make mention of some hidden sacraments connected with the descent of the Onlybegotten from the bosom of the Father.

I assume as firmly established what the holy faith teaches in regard to the Divine Persons, that although there is a real personal distinction between the three Persons, yet there is no inequality in wisdom, omnipotence or other attributes, just as little as there is in the Divine nature; and just as They are equal in dignity and infinite perfection, so They are also equal in these operations ad extra*, which proceed from God himself for the production of some creature or temporal object. these operations are indivisibly wrought by three Divine Persons; for not one Person alone produces them, but all Three in so far as They are one and the same God, possessing one and the same wisdom, one and the same understanding and will. Thus what the Son knows and wishes, that also the Father knows and wishes; and so also the Holy Ghost knows and wishes whatever is known and willed by the Father and the Son.

In this indivisibility of action the three Persons wrought and executed, by one and the same act, the mystery of the Incarnation, although only the person of the Son accepted for Himself the nature of man, uniting it to Himself hypostatically. Therefore we say that the Son was sent by the eternal Father, from whose intelligence He proceeds, and that the Father sent Him by the intervening operations of the Holy Ghost. As it was the Person of the Son which came to be made man, this same Person before descending from the heavens and the bosom of the Father, in the name of that same humanity to be received by Him, made a conditional request, that, on account of His foreseen merits, His salvation and satisfaction of the Divine justice for sins be extended to the whole human race. He desired the fiat or ratification of the most blessed will of the Father, who sent Him, for the acceptance of this Redemption by means of His most holy works and His passion, and through the mysteries, which He was to enact in the new Church and in the law of grace.

The eternal Father accepted this petition and the foreseen merits of the Word; He conceded all that was proposed and asked for the mortals, and He Himself confirmed the elect and predestined souls as the inheritance and possession of Christ forever. Hence, Christ Himself, our Lord, through saint John says that He has not lost nor has allowed to perish, those whom the Father had given Him(John 18,9). In another place it is said: that no one shall snatch his sheep from His hands nor from those of His Father (John 17, 12). The same would hold good of all those that are born, if they would avail themselves of the Redemption, which, as it is sufficient, should also be efficacious for all and in all; since His divine mercy desired to exclude no one, if only all of them would make themselves capable of receiving its benefits through the Redeemer." ~Venerable Sr. Mary of Agreda

*Note: In Trinitarian theology, the phrase “equal in these operations ad extra” refers to how the Father, Son, and Holy Spirit—though distinct persons—act with perfect unity and equality in all external works (Latin: opera ad extra) such as creation, redemption, and sanctification. The Trinity’s external operations are inseparable and undivided, meaning all three persons are involved in every divine action outside of God, though each may be revealed differently in those actions.