@Setanta,
Set, the "spirit within" thing signifies the democratization of God.
No longer did a person have to go to a priest in the Holy of Holies to speak to God and get absolution.
Whether if God exists or not the democratization of God gave less church control over the believer/non believer.
That meant the believer could make intercession for themselves.
When God speaks from clouds, burning bushes or though priest, the spirit is upon them.
When one priest confers the spirit to another priest he transfers the mantle. The mantle ceremony a physical representation of the transference of the spirit upon one priest and being conferred to another. (yea, Humpty Dumpty)
"Upon" what condition?
The spirit was granted upon the conditions that one followed the law and believed in the holy spirit.
Can the spirit be removed? Well it seems so in passing the mantle.
But the idea is that spiritual "seed" cannot be removed.
Seed is an eternal truth.
Born once of physical seed and "born again" of spiritual seed.