The Triune God

Yesterday was Trinity Sunday. As a convert to Catholicism from Mormonism, the whole notion of the Trinity was one that took some time to fully wrap my head around. However, at this point in my career I feel confident that I not only understand it better than most, but I am also in the process of doing research on how others (specifically Mormons) view the Trinitarian relationship.
So it seems to me that this deserves some attention. The early Christians faced several difficult challenges in defining the Trinitarian relationship. The Arians thought that Jesus couldn't be God, but only human. The Manicheans separated Jesus' humanity from His Divinity.
But it goes back further than that. The early Christians were faced with the difficulty of believing somehow that Jesus was a lot more than a human being. The Gospel of John makes Jesus out to be God. The opening words are "In the beginning was the Word, and the Word was with God, and the Word was God." Thus the tone of Trinitarian existence is set forth from even the first century.
The gospels all set out the tone of Jesus being God. Then comes the Acts of the Apostles. With Pentecost (last week, by the way), the problem of the Holy Spirit comes onto the scene. Whereas the issue of Jesus' Divinity is somewhat problematic, especially with His unity with the Father, the Holy Spirit is a whole new problem all together. Who is this Holy Spirit that does not enter the scene (apparently) until at least Jesus' baptism? After much discussion, and careful prayer, the early Fathers decided that the Holy Spirit must also be God, and also unified with the Father and the Son.
But as most who have taken a basic course in Christian Theology or Sunday School know, the official stance of the Trinitarian formula was not fully developed until the Early councils, especially Nicaea and Chalcedon.
The one tragic part of the Trinitarian doctrine is that the more it was explained and developed, the more people that became Anathema. The Arians, the Manicheans, the Coptics, the Syriacs, the Assyrians, the Chalcedonians, the Nestorians (I apologize), the Maronites, and eventually the Orthodox Church all eventually were cut off from the Roman Church. Ideas such as the theotokos (God bearer), homousious, and the phrase "proceeds through the Father and the Son" as opposed to "proceeds through the Father through the Son" became operative in the the schismatic process.
Similarly, my sister yesterday went with me to Mass and liked to interject at every point that she thought that the doctrine supported her views. That's the real problem. The Trinity is such a blessed mystery that a lot of ways that we use to describe the relationship murkies up the water. Nobody who claims to be God has completely anti-Trinitarian views on the subject, but a lot of the explanations vary.
I think that St Augustine, one of my personal favorites among the philosopher/theologians and a Doctor of the Church explained it best. He described the relationship thus: the Son is God's word, eternally proclaimed, from time immemorial even until now. The Holy Spirit is the love shared between the Father and the Son. The Love is emitted from God to us, the Son is eternally proclaimed to us and the Father is eternally reigning over the heavens and earth.
This is not an easy notion to understand. However, to be fair, I do not believe that having a perfect understanding and knowledge of the relationship of the Father, Son and Holy Spirit is necessary for our salvation.