Which brings us neatly back to square one again: who, then, is left to populate the millennium? If it is only the redeemed who enter into it, then whence cometh the rebellion at the end of this glorious reign of the Messiah? A mass revolt which Satan somehow manages to organize from 'the four corners of the earth' despite the personal reign of the glorified Christ over his own sheep?
Do all the sheep decide en masse at the end of their Saviour's personal reign that they've had quite enough of this malarkey, and it's about time that they put those doctrines of grace to the test? Giving a convincing anthropological description of the 'millennium' that satisfies all of its salient features is just one of many problems you face with your materialistic interpretation, and when you have figured out the answer, by all means let us know.