"How many persons are there in the Trinity?"
"All of us!"
It's always good to give the teacher something to think about; it puts her off the track for a while. But this one wasn’t intended; it was the wisdom that comes "out of the mouths of infants and nursing babies" (Matthew 21:16).
But isn't it only three? Yes, three Divine Persons - but all of us too, as the child said. We live in God. We are more accustomed to saying that God lives in us, but it is equally true that we live in God.
If you have a jug of water, said Meister Eckhart (14th century), and you pour it out, it is now outside and no longer inside the jug. Before we came into being we existed in the mind of God. Then when we came into being we were "poured out", as it were. Does this mean that we are no longer "in God"? The image of water being poured out would suggest so. But that image is a fully material one and not up to the job of throwing light on this subject. Think instead of knowledge and love. When you know something, that knowledge is of course in your mind, "within" you. Then you share it, you pour it out: to a few friends, or perhaps to many people, like a teacher. It poured out, but it still remains within; you have imparted it but you not parted with it. Likewise with love: when you give your love to someone, you do not lose it; in fact it is only in giving it that you have it. In some such way, when we come into being, we are "poured out" from God, and yet we remain within. A child is able to speak the truth in a direct and immediate way, with none of our complicated explanations: we are living in the Trinity.
Another 14th-century saint, Catherine of Siena, wrote: "The soul is in God, and God is in the soul, as the fish is in the ocean and the ocean in the fish." It is exaggerating greatly to saya that the ocean is in the fish, because only a couple of cubic centimetres of it are in the fish's gills at any time. But it is as far as a material image will take us. We want to say that all of God is in the soul. God doesn’t have parts, so wherever God is, all of God is there. All of God is in me and all of me is in God. This is a useful thought on days when you feel lost and lonely.
If you were to ask a fish to point to the ocean, it would have to point in three directions: up (or down - anyway, you know what I mean; you are good enough even to tolerate me when I speak about a fish 'pointing'!); it would also have to point all around; and (remembering those cubic centimetres) it would have to point in. We too, when we want to point to God, have to point in three directions: up (or down, if you prefer to think of God as in depth), out and in. We point up to God our Father (from childhood our neck muscles tell us the look up at our fathers and mothers); we point out (at eye level, so to speak) at the Word made flesh who has become like us in all things but sin; and we point in at the Holy Spirit who lives within us, for we are "temples of the Holy Spirit."
Of course all this is very imprecise language, but if it stimulates you to reflect and meditate on the supreme mystery of God, Three in One, it serves its purpose. It is the people who have penetrated furthest into the mystery of God - the mystics - who keep repeating that all language is inadequate to express what they have experienced. "Stammering," they have called it. But why should lit be so difficult to talk precisely about the Trinity. If the mystery was revealed to us, why shouldn't it be crystal clear? Was it badly revealed, like a blurred photograph? It is not that. If it is difficult to talk about the Trinity, this is because the Trinity is not just for talking about. "I bind unto myself today / The strong name of the Trinity," says the hymn (St Patrick's Breastplate). "I bind unto myself today / The power of God to hold and lead." The Trinity is for living; we want to give every part of our being to God, not only our mind. When we read the newspapers, the mind is involved while the rest of our being is just sitting back. The Trinity is for living, because we are involved in it; we are in it. "All of us."