The three persons of the Trinity coexist eternally, but not in the same way that other things coexist, mainly because these three are infinite, and not external to each other. And one of the Trinity, the eternal Son, took human nature into union with himself

Thomas Aquinas’ treatise on the Trinity in the first part of his Summa Theologiae runs from question 27 to 43. It’s a vast discussion, all but comprehensive in its coverage of the most important elements of Trinitarian theology. So sweeping an account could start from

When speaking of the Trinity, you can say three, but you can’t say triple or threefold or triplex. And you certainly shouldn’t say that the Father, Son, and Holy Spirit are three beings. In these two axioms, Polanus is largely covering ground he has already

I like this compact account of Trinitarian terminology in Vladimir Lossky’s Dogmatic Theology, 38-40. It’s especially good at showing the relation between the words ousia and hypostasis. Watch how Lossky relates the key terms to each other and uses them to draw out how they

In trinitarian theology, the word “mission” is a precise and technical term. Though the word itself just means “sending,” a trinitarian mission is the external personal operation of one of the Trinity. It presupposes something very important, and that is an eternal relation of origin

I think it’s fair to say this will not be one of the easier episodes, because Polanus lays out quite a bit of difficult material here, and it’s all interconnected. We are nearly done with the very long Axiom 14. This sub-section of the axiom

Tropos hyparxeos! Polanus comes to the point where he is ready to teach about the distinction of the persons from each other, and he invokes Cyril and Aquinas as authorities in affirming that the distinction among the persons ought to be the smallest of distinctions.

Perichoresis! So hot right now. Actually, so hot all the time. The confession that the persons of the Trinity mutually indwell each other –“I am in the Father and the Father is in me”– is directly evident from Scripture, has been confessed in the church

One of the things you can say about the divine persons is that they are equal with each other. Right between affirming their consubstantiality and their mutual indwelling, Polanus devotes a couple of paragraphs to affirming their equality. “The three persons are equal among themselves

In the journey through his long 14th Axiom, Polanus has one last thing to say about how we should speak of a person of the Trinity in relation to the divine essence. What he wants to say is that we should avoid weird sentences like

In this section –one sub-section of Axiom 14– Polanus focuses on a difficult task. He intends to show how to speak responsibly about a divine person in relation to the divine essence. What’s difficult about that is that a divine person just is the divine

Polanus’ eighteen Axioms on the Trinity are mostly pretty short, but Axiom 14 stands out for its length and comprehensiveness. It’s as long as the other seventeen put together (3,000 words out of the total 6,000), and it covers a lot of ground. It will