well they said no one would be able to trade or sale, so I guess people interpret that as some sort of electronic identification/economic device
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But for your last point, people change their religious beliefs all the time, even without "magic tricks", not that the Bible mentions any out side of the false resurrection of the beast (correct me if i'm wrong).
But since we're talking about a story in the bible, lets go by what it says looking at it as a whole.
It says even the elect would be deceived
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The best way to control people is not by physical action, but belief. Think about it....