You can also explain it this way. Ask if they have a very good friend, someone who brings out the best in them. Ask if their mom and dad are like that…that is, you can’t really know one unless you know both.
Explain that understanding how the three Persons of God can be distinctly three and yet absolutely one is only difficult to us because we do not understand love very well yet. When we love as God intends us to, with God’s love instead of with our little human love, we become both more ourselves and more unified with the needs of those around us. We become more distinct, but more unique–more unmistakeably Jake and Maria and Brandon and Jessica–and yet more one with those we love, too.
We can see this in the lives of the saints. Each one is so different. That is because learning to love is how we become our unique selves.
Thus, the mystery of the Trinity isn’t just some fact we need to learn. It is a life we must learn to live. It is what Christianity is all about:
“I do not pray for them alone. I pray also for those who will believe in me through their word, that all may be one as you, Father, are in me, and I in you; I pray that they may be one in us, that the world may believe that you sent me. I have given them the glory you gave me that they may be one, as we are one–I living in them, you living in me–that their unity may be complete. So shall the world know that you sent me, and that you loved them as you loved me.” John 17:20-23
This is also why those who do not know how to love cannot have Heaven, for to be in Heaven is to be absolutely abandoned to love. Eternity is the greatest happiness for those who love, and the greatest torture for those who will not. If you prefer sin instead of love, then that sin is something you hold on to. You hurt to lose it. The thing is, everything that is not love will burn away in eternity. When all that is burned away, the person who cannot love as God does, who cannot find joy in giving of themselves, is left with nothing.
What a great thing, though, if love is the center of all, as it will be in Heaven! No misunderstandings, no worrying about getting enough or who doesn’t like you or whether you’re good enough. You love everybody, everybody loves you, and nothing you ever experience is ruined by hurt feelings. Every smell, every taste, every sound, every sight can shine brightly and be enjoyed fully. You will be full of joy, praise, and thanksgiving for every good thing that comes from God.
And do you know what? That can start now. Think about it. If you are thankful, doesn’t the ice cream taste better? If you are getting along with your friends, when no one is worried about who gets the credit or who is the center of attention, aren’t all the games more fun? If you have nothing to feel guilty about, isn’t your heart light and carefree?
That is what Jesus meant when he said the Kingdom of God is at hand. Heaven is there, today, waiting for us to love and to join into it. The easiest sin is harder on us and hurts us more in the end than the hardest kind of love…we just have to believe that and let God convert us over to that way of seeing. Even when it is hard to love, we are never lost in love. We are always found. That is what living in the Trinity has to teach us.
I have asked first graders if they are going to be saints some day. A good fraction will say “no.” I say, oh, if you’re going to heaven, you can be certain that God is going to make you into a saint! I guarantee that you are going to love it! No saint ever looks back and says, “Oh, I would have enjoyed going on sinning awhile longer.” No, once they leave, they never want to go back. So since that is where you are going, and since it is better than where you are now, you may as well let God get started…today!
That is, after all, what a mystery is. It is something you only know by living it. The mystery of the Trinity can only be truly known by those who are one with God. To everyone else, it is only a puzzle.