For those who believe Jesus and God and Holy Spirit are all ONE, why would you think we still need to pray?

Because He says we must pray. Its what brings us closer to Him. Prayer causes things to happen that will not happen if we never pray. In fact Jesus said that we must pray without ceasing. I don't know who this God is that you are talking about. He isn't in the bible. But He seems to be created in your mind. That is why your statements don't make any sense and there is no logic in what you are talking about as far as who the real God is. He is the God of the bible. And the bible clearly explains who He is.