What we know of God, the Judeo-Christian God we know from the Bible. The conclusion is that ours is a revealed knowledge, God Himself the reveal-er. Without getting into the separation between the Jews and the Christians and the ancient debate between the Old Testament (The Torah) and the New Testament I'll try and cover some of the basic concepts and when I have a little more time, come back to this topic.

Christians believe that all scripture is given by the inspiration of God, i.e. The Holy Spirit inspired human writers to write what they did. Many of us, for that reason, hold the Bible as our only source of authority. One of the great schisms between Protestants and Roman Catholics is that the Catholics hold that when the Pope speaks ex-cathedra (from the throne) his word has equality or ascendancy over scripture.

Genesis 1 speaks of the Spirit of God brooding over the face of the deep during creation. There are many instances of His Spirit in the OT as well as what are known as epiphanies where God has come to certain persons in bodily form. The story of Abraham on the Plains of Mamry is one of the most notable instances. When Jesus was baptised, John saw the Holy spirit descending as a dove or like a dove. At the same time a voice came from heaven saying "this is my beloved Son in whom I am well pleased." This presents a picture of what is termed the "Trinity" though THAT word never appears in scripture. Elsewhere Jesus teaches that God IS a Spirit and that God is Love. He goes on to describe the extent of that Love toward a lost and dying Humanity. When the disciples asked Jesus to show them the Father, Jesus replied "He that hath seen me hath seen the Father. This is the essence of the mystery of the Godhead, the Three in One. All are present in the Son, in the Father and the Holy Spirit. The Bible teaches that God is omnipresence and also that all things consist by Him. He, His Spirit holds the universe together and He is everywhere in the universe but He is NOT the universe: IT is his creation.

Jesus said that all manner of sin and blasphemy against the Father and the Son may be forgiven but blasphemy against the Holy Spirit cannot be forgiven. This is known as the unpardonable sin. When Peter made his great confession of faith and declared that Jesus was the Son of the Living God, Jesus said "Blessed are you Simon, son of Jonah (Peter was his nickname and actually translates "Rocky") for flesh and blood has not revealed this to you (that is the physical man, Jesus) but my Father which is in heaven." The reason that blasphemy against the Holy Spirit is unpardonable is that once Christ (which means "The Anointed One" i.e. anointed by the Holy Spirit) is revealed for who he really is to your soul, God has done all He will ever do to offer you salvation. If you reject Him after such a revelation there is nothing more He can do or perhaps that He will do. This doesn't mean that you can't opt later but your soul is at great risk at that point. Compare this thought with John chapter 9 and especially verse 37 to the end.

There are some very interesting etiologies of the word "spirit" (Greek "pneuma" and Hebrew "nephesh") and the development of the Occidental mind but those are really just asides. I hope I have shed a little light on the fundamental Christian perspective on the question.