I find it difficult to preach on Trinity Sunday. Standing in the pulpit and admitting that I do not understand something does not seem like a good idea. Not much Gospel in such an admission. So what is the preacher to do this day? It seems like you might have several options.
Preach Baptism – we are after all baptized into this Trinitarian name. We are united to a great mystery in that water and Word.
Preach the Economy of Salvation – We can only tell the Father from the Son because the Father sent the Son to die on that cross for our sins and be raised for our justification. The Father did not die. The Spirit did not die. Only the Son died. Likewise the Son did not send the Father. The Father sent the Son. The Spirit alone was poured out. Outside this work of salvation, we only experience the unity of God. In saving us, he has revealed himself most intimately.
Preach Humility before God – The fact that we cannot grasp God makes us more confident of what we believe. After all, wouldn’t a god you understood be a pretty small god? My failure to understand God is good news of a sort, but only when my flummoxed self stands before the cross. Keep it there.
Most of all, preach Christ crucified – the Son of the Father, the object of the Spirit’s work but Christ crucified. Below is a photo of El Greco’s depiction of the Trinity. The original is in the Prado museum in Madrid.