Today is Trinity Sunday.
On this feast day, in 1858, Venerable John Henry Newman, C.O., preached a sermon, of which the following notes survive:

The Blessed Trinity

1. INTROD.—This is the everlasting mystery. All other mysteries arise in time, this in eternity.

2. No words of man can explain it. Three are one. Now soul and body are one, all the faithful are one. The soul, when enveloped in the Divine Essence, hereafter is one with it. But no illustration of earth can give the faintest shadow of the truth.

3. Yet though so difficult for the reason, it is not difficult for devotion, and thus is fulfilled the saying, 'Thou hast hid these things from the wise and prudent, and revealed them to Thy little ones.'

4. For each truth concerning the Holy Trinity is easy. It is their combination is the mystery. Exemplify. That there should be one God—that God should be called or be the Father—that He should be the Son—that He should be the Holy Ghost—but that all three propositions [four] should be true .

5. Explain more fully. The Father is absolutely the One God, as if no Son and Spirit, etc. All the attributes, etc. belong to the Father, and to the Son, etc. Whatever the Father does or is, that the Son does or is—not as two, but One.

6. But they divide offices in mercy to our infirmity.

7. Now for devotion. The Father, the Creator, the Preserver, Governor, Judge. Source of all good; the harbour of our rest; heaven, etc.

8. The Son has taken on Him our nature, etc.

9. Holy Ghost Sanctifier, etc.

10. Now while we address each in devotion as the One God, we may leave it to the next world how Each of Three can be the One God.

11. The joy of heaven, when all mysteries will be removed.