Eamonn Clark

The story goes that an old Irish priest was getting ready for his homily on Trinity Sunday. In Ireland at the time, on this Feast, the annual tithe of peat moss was made, to supplement the priest’s salary. He would need it for the fires throughout the coming winter. He ascended the ambo to preach that Sunday, and said, “As you know today is Trinity Sunday. That means it’s time to make the tithe of peat. If I don’t have peat, the winter will be dreadful, etc.” When asked later by a friend why he didn’t preach on the Trinity, the priest said, “Well, they all believe in that… They don’t all believe in making their tithe of peat!”

It should go without saying that, being the highest Mystery of our Faith – God Himself – the Trinity matters. However, as Rahner aptly pointed out in his important book on the subject, the Trinity has nonetheless somehow been slipping into practical irrelevance in the lives of believers. One must ask not only whether people do not believe in “tithing peat” and other such appropriate responses of parochial commitment anymore – but if they even really believe in the entire center and ultimate point of Christianity, which is the Triune Godhead as such. Or, instead, is it the case that, after so many preachers simply assuming “they believe it,” they are rather actually some kind of Sabellians or Arians, even if unknowingly? (Many are.) What effects could that have on the spiritual life, for individuals, and also for the whole Church and world? (Enormous ones.) And what exactly is the doctrine of the Trinity anyway? (Three Persons in One God.) Is it even really coherent? (Yes.) Is the doctrine demonstrable from reason alone? (No.) Do the missions imply a subordination of the Persons? (No.) Etc.

We will be walking step by step through the Treatise on the Trinity by St. Thomas Aquinas in the Summa Theologica, starting with Question 27 of the Prima Pars and going all the way through to Question 43… At the end, I will introduce you to the most relevant debate occurring right now in Trinitarian theology (over Rahner’s famous “grundaxiom” – “The Immanent Trinity is the Economic Trinity, and the Economic Trinity is the Immanent Trinity”) and perhaps give some additional reflections on the visible mission of the Son (the Incarnation) as it relates to the mysteries of His public life and ministry.

Have no fear! I will break down the language piece by piece and sift through all the normal queries. As St. Augustine said, this part of theology is the most dangerous, but it is also the most fruitful… It’s worth the effort.

Astute and zealous readers might want to brush up first on Divine Simplicity (Question 3) to see what is immediately at stake in this topic (basically, if something is not perfectly simple, viz., without parts, then it’s not God – such a thing would have had to be put together by something else which existed prior to it). Other Questions might be helpful to read too (11-14, 18-20, 22, 25), but Question 3 is enough to see the major “obstacle” at hand. I will help you through the rest.

I hope you enjoy this upcoming series, and may God the Father, God the Son, and God the Holy Spirit bless you and keep you always… Happy Trinity Sunday!

Main image: The Jordan River, near the Baptismal Site, the lowest place on Earth – where all Three Persons were encountered by distinct visible missions.