All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit [Matthew 28:19].
These are the words of Jesus. Jesus is the final atthourity in all things related to God's relation with people.
Does that mean that the holy spirit exists as an entity? Could it be possible that the holy spirit is in the minds of the beleivers?
Is Ghost the same thing as Spirit?
I am not saying the Holy Spirit is not part of the God Head. I am saying it is a concept that is open to speculation and personal opinion. The Menninites, Methodist, and Baptists were formed by people that did not beleive in the trinity. I believe their main point was adult baptism. Hence the name Baptist.