God the Holy Ghost testifies of the father and the son. He testifies of all truth. He comforts. He teaches. He is differentiated as ghost or spirit because he is the only member of the Godhead who does not have a physical body.
The Holy Ghost
These are topics I have collected scripture references (the words of apostles and prophets) and posted in this blog for others to study and pray about for themselves that we all may be edified and grow. My own comments have also been added to pull the reader's eye toward what I think I saw in those words.