This is what I was told by my pastor, who is Calvinist. I asked him how that worked, or what it meant in the light of the clear teaching of Preservation of the Saints...
He told me 1) I didn't have to worry about it because only the people around Jesus at the time could do it.
and 2) a christian cannot blaspheme the HS, period.
He said that Jesus said this after the pharasees had accused Him of putting devils out of the people with Satan's authority, not God's. So to blaspheme the HS is to attribute the miracles of Jesus as being done with the power of the devil.
Now, I'll admit, it really threw me for a loop here, because I have never heard that at all, but, it does sort of make sense. That perhaps it was spoken to the pharasees of the day, who were seeing with their own eyes the miracles of Jesus and STILL denying Him.
What does everyone else think? I'm not sure if I explained it very well...so if I need to explain it better, let me know....