There are precious few scriptures describing the nature of the Holy Ghost. Nephi's vision is one of them. The Spirit is the third member of the Godhead. He has the form of a man, but no body. He was chosen in the premortal life to stand next to the Father and the Son and bear witness of them to us during our mortal journey. He is also called The Comforter. Through him, God's love and influence can be felt in more than one place at the same time. It is not inhibited by physical barriers. Actually, whether we feel his influence or not is more about us and less about the Spirit. Like the Father and the Son, he is constant, unchanging. His voice is always there, waiting to be heard and sought out. We are the ones who move, either toward his voice or away. We should cultivate a spiritual ear tuned to listen to his still, small promptings.
Nephi was given a sacred experience: a personal face-to-face introduction to the voice he had been listening to.