One of the most difficult to explain, and often misunderstood concepts in the Christian faith is the belief in a trinitarian God, one God with three aspects. Often characterized as the 'Father,' Son,' and 'Holy Spirit,' the trinity represents God the Father/Creator, Jesus Christ the Son and Savior, and the Holy Spirit, or the creative, inspirational force at work in the world.
It is this 'three-in-one' characterization of God that some point to as contradictory to the doctrine of there being one and only one God, that somehow Christians pray to more than one god. Christian teachings and belief however are clear on this point: there is only one God, the Creator of the universe, who has three 'persons' or aspects, inseparable yet unique parts of the whole.
There are many metaphors for the Trinity, many ways of trying to conceptualize that which is almost beyond our grasp, but for Christians it is the way we interact with these three aspects that matter most. The Trinity provides structure to our prayers, our worship services, our lives.
The Father
Genesis describes the creation of the world thus:
"In the beginning when God created the heavens and the earth, the earth was a formless void and darkness covered the face of the deep, while a wind from God swept over the face of the waters. Then God said, "Let there be light"; and there was light. And God saw that the light was good; and God separated the light from the darkness. God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day." Genesis 1, from The New Revised Standard Version, copyright 1989 by the Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.
This is the aspect of God we call the 'Father,' though it is generally accepted that we're really referring to the 'parent,' as God is seen as neither male nor female. This is the creative, nurturing, loving aspect of God, the One who brought the world into being and who created humans "in the image of God..." This is the God whom the Iraelites saw as the one true God, the One who provided for them, and who cared for (and disciplined) them.
The Son
One of the promises that God the Father made to Israel was that a messiah (leader, teacher, saviour) would come into the world to bring all humans into full relationship with God. As Christians we believe that this messiah came in the form and person of Jesus, born as a human. Though fully human in body, most Christians believe that the spirit of Jesus was that of God itself. This represents the second aspect of the Trinity, Jesus Christ the 'Son.'
What this means to Christians is that while we embrace the teachings of Jesus the man, while we strive to emulate his life and works, we also pray to Jesus as God to intervene in the world and our lives and give us the strength and forgiveness to live our lives according to those teachings. Jesus also acts to speak on our behalf with God the Father, asking for His intervention in the affairs of the world and forgiveness for the failings and 'sins' of humans.
The Holy Spirit
Perhaps the most difficult aspect of God to explain is that of the Holy Spirit. This is the aspect of God that is at work in the world, that inspires us, that speaks to us and strengthens us to do the often difficult work that our faith demands of us. The Spirit is often seen as the creative energy that's at work in the world, whereas God the Father 'willed' the world to come into being, God the Holy Spirit was the force that brought this into being.
A wonderful description of the Spirit is given in the apostle Paul's letter to the Corinthians:
"...What no eye has seen, nor ear heard, nor the human heart conceived, what God has prepared for those who love him, these things God has revealed to us through the Spirit; for the Spirit searches everything, even the depths of God. For what human being knows what is truly human except the human spirit that is within? So also no one comprehends what is truly God's except the Spirit of God. Now we have received not the spirit of the world, but the Spirit that is from God, so that we may understand the gifts bestowed on us by God. And we speak of these things in words not taught by human wisdom but taught by the Spirit, interpreting spiritual things to those who are spiritual." 1 Corinthians 2:9-13
These three 'persons' integrate into the one that is 'God' who is beyond these distinctions. Just as we ourselves consist of body and mind and spirit (among many other ways of subdividing the parts that make up the whole) these three aspects of God in combination represent God to the world in general and to humans in particular.