I'm not a theologian, just a teacher. But we all know teachers think they have an answer to ANY question, so...
The doctrine of the Trinity has been a cornerstone of Christian faith for centuries. It is a man-made term used to decribe a God who is undescribable. If you want to read an exhaustive description of the Trinity, google "The Athanasian Creed". That was the church's attempt to describe a God that is beyond description. (It is rubbish in my opinion because I feel that God is beyond our senses and therefore cannot be described. "Transcendental" as the great philosopher Immanuel Kant would say.)
Basically as I see it, the Holy Spirit is God, along with God the Father and Jesus the Son. All are equally God and fully God. The three great works of God are creation, redemption (chiefly the life death and resurrection of Jesus) and sanctification (the working of God in our lives).
The Holy Spirit is the aspect of God that primarily deals with sanctification. The HS is the force that works faith in us, strengthens us in our lives and leads us to do acts of love toward God and for others.
The Holy Spirit is sort of the "electricity" of God. He/She is the power that is at work in people. On the day of Pentecost the disciples were filled with power at the coming of the Holy Spirit. God's grace, the love shown to all people, comes to us through the life, death and resurrection of Jesus by the power of the Holy Spirit. Without the Holy Spirit we would not have a connection to the "transcendental" God. We would not be able to have the grace of God in our lives or be able to share that grace with others.
This is a far from perfect answer to your question. I don't know if Protestant churches view the Holy Spirit differently, but this is the basic understanding of the Catholic, Episcopal and Lutheran churches. (Lutheran and Episcopal churches are sort of protestant, sort of not. They can't quite decide.)
For I am convinced that neither life nor death...neither the present nor the future nor anything in all creation will be able to separate us from the love of God that is in Christ Jesus our Lord. Romans 8:38-39
Last edited by Pablo Rafael; 09-05-2009 at 08:48 PM.
Reason: correct all those typos - should be a law against them.