Father~Son~Holy Ghost. Who is the Holy Ghost? Is this not God?
Paul calls the Holy Ghost (or more properly, the Holy Spirit) the word of God in Ephesians 6:17. This is more than just the words written on the pages of our Bibles. It encompasses all the power of God in his word. Just to show how much power that is, God spoke and the world we know came into being. The word of God in us is our proof that we have been saved.
Is the Holy Spirit God? That is a difficult question. Some have presented a doctrine of the “Trinity,” which is not directly taught in the Bible. (Please see my answer at What Does the Bible Say About..The Trinity? for more details.) To ask if the Holy Spirit is God is like asking if the words I write are me. They can not exist unless I bring them into being. They are certainly expressive of who I am. You can not separate them from me. But I also have an existence without having written or spoken anything. So it is with God. He exists. He would exist even if he had never found a need to speak. But his word, the Holy Spirit, is expressive of God. He shows us who God is, and speaks for us to God. He does not exist without God, but can not truly be called a creation of God. Does this make him God, or not God? I can’t say for sure. But it is not something I need to know for sure, because God hasn’t made it clear. He has “given us all things that pertain to life and godliness.” (1 Peter 1:3) Since he hasn’t made this clear then it clearly is not essential to life or obeying God.