The Shield of the Trinity

Sometimes (okay, IMO, often) Wikipedia is a great place to start!  Most of the articles are very well researched and don't have a bias.  Here is their article on The Trinity  and  here is their article on this diagram, The Shield of the Trinity, which is considered to be the best way to illustrate something that is pretty much not able to be illustrated!

Andrei Rublev's The Trinity

This icon by Andrei Rublev is perhaps the most famous image of The Trinity. 
The Father is represented in the figure on the left, the robes He wears are primarily gold, representing His Kingship and royalty.
Jesus, the Son, both fully Divine and fully human wears brown, the color of the earth.  The Spirit on the right, wears both blue and green to symbolize the Spirit's moving through both sky and water. 
Notice the rectangle at the table, between the Father and the Spirit?  Historians believe that at one time there was a mirror there, inviting a fourth person to the table.  Inviting us to to join in the divine circle of love that is God. 
Here's more information about this icon. 

Great Sermon

Day1.org is a wonderful resource, full of great sermons and articles from mainline Protestant preachers.  This one, The Dance, is especially cool.  And so is this one, I'll Tell You When You're Older.  You can read them or listen.

Great Book! Read it Now for Free (with your library card from any library in Allegheny County)

The Divine Dance is one of the best books I've ever read on the Trinity.  Written by Father Richard Rohr, a  Franciscan friar based in Albuquerque, New Mexico, it really pulls in the history of the doctrine and gives great insight into the ways in which we think about God as Trinity can transform our way of looking at the world and living out our faith.

Quotes on the Trinity

"We are now eager to see whether that most excellent love is proper to the Holy Spirit, and if it is not so, whether the Father, or the Son, or the Holy Trinity itself is love, since we cannot contradict the most certain faith and the most weighty authority of Scripture which says: 'God is love'" - Augustine, On the Trinity, begun in 400 CE

“The Trinity is unity in diversity; the Trinity is our model for community.

When I think of the phrase The Coming of the Kingdom it means to me a restoration of community, the healing of brokenness which will enable us to rejoice once more in being one – not solitary, isolated one, but whole, body, intellect, spirit at peace; mind, heart, intuition in collaboration.

There are those who do not want this wholeness, who want to continue the process of fragmentation, and this has to be fought, with Michael and his angels by our side. If we care about wholeness, about unity in diversity, we are in battle.”

– Madeleine L’Engle, The Irrational Season, 1977

It is commonly said that the Trinity is a mystery. And it certainly is … . But it is not a mystery veiled in darkness in which we can only grope and guess. It is a mystery in which we are given to understand that we will never know all there is of God … . It is not a mystery that keeps us in the dark, but a mystery in which we are taken by the hand and gradually led into the light … – Eugene Peterson, Christ Plays in Ten Thousand Places, 2005

All sorts of people are fond of repeating the Christian statement that ‘God is love’. But they seem not to notice that the words ‘God is love’ have no real meaning unless God contains at least two Persons. Love is something that one person has for another person. If God was a single person, then before the world was made, He was not love. Of course, what these people mean when they say that God is love is often something quite different: they really mean ‘Love is God’. They really mean that our feelings of love, however and wherever they arise, and whatever results they produce, are to be treated with great respect. Perhaps they are: but that is something quite different from what Christians mean by the statement ‘God is love’. They believe that the living, dynamic activity of love has been going on in God forever and has created everything else.

And that, by the way, is perhaps the most important difference between Christianity and all other religions: that in Christianity God is not a static thing—not even a person—but a dynamic, pulsating activity, a life, almost a kind of drama. Almost, if you will not think me irreverent, a kind of dance. The union between the Father and the Son is such a live concrete thing that this union itself is also a Person. I know this is almost inconceivable, but look at it thus. You know that among human beings, when they get together in a family, or a club, or a trade union, people talk about the ‘spirit’ of that family, or club, or trade union. They talk about its ‘spirit’ because the individual members, when they are together, do really develop particular ways of talking and behaving which they would not have if they were apart. It is as if a sort of communal personality came into existence. Of course, it is not a real person: it is only rather like a person. But that is just one of the differences between God and us. What grows out of the joint life of the Father and Son is a real Person, is in fact the Third of the three Persons who are God.

This third Person is called, in technical language, the Holy Ghost or the ‘spirit’ of God. Do not be worried or surprised if you find it (or Him) rather vaguer or more shadowy in your mind than the other two. I think there is a reason why that must be so. In the Christian life you are not usually looking at Him. He is always acting through you. If you think of the Father as something ‘out there’, in front of you, and of the Son as someone standing at your side, helping you to pray, trying to turn you into another son, then you have to think of the third Person as something inside you, or behind you. Perhaps some people might find it easier to begin with the third Person and work backwards. God is love, and that love works through men—especially through the whole community of Christians. But this spirit of love is, from all eternity, a love going on between the Father and the Son. – C.S. Lewis, Mere Christianity, 1952

The all-powerful truth of the Trinity is the Father, who created us and keeps us within him. The deep wisdom of the Trinity is our Mother, in whom we all are enfolded. The exalted goodness of the Trinity is our beloved Lord: we are held in him and he is held in us. We are enclosed in the Father, we are enclosed in the Son, and we are enclosed in the Holy Spirit. The Father, the Son, and the Holy Spirit are enclosed in us. All Power. All Goodness. All Wisdom. One God. One Love. — Julian of Norwich, Fourteenth Revelation, Chapter 54, circa 1370