Is the Holy Ghost different in Mormon theology than in Christian theology?
Yes. Though the Holy Spirit is not spoken of much in Mormon theology, He has nonetheless gone through some changes of His own in their theology. The first thing I would like to note is that the LDS believe that spirits are lesser beings than those with bodies, since having a body is the only way that one can become a god and increase their own glory. The problem that Mormons run into is that they believe that the Holy Spirit is a god already, and did not need to have a body in order to do that. This instantly conflicts with their own doctrines. This is what the Mormons believe concerning the Holy Spirit. Joseph Smith taught the following: “I have always declared God to be a distinct personage, Jesus Christ a separate and distinct personage from God the Father, and the Holy Ghost was a distinct personage and a Spirit: and these three constitute three distinct personages and three Gods. If this is in accordance with the New Testament, lo and behold! we have three Gods anyhow, and they ar