St. Augustine was for a time, as he himself testifies (City of God XX.7), a pronounced champion of millenarianism; but he places the millennium after the universal resurrection and regards it in a more spiritual light (Sermo, CCLIX). When, however, he accepted the doctrine of only one universal resurrection and a final judgment immediately following, he could no longer cling to the principal tenet of early chiliasm. St. Augustine finally held to the conviction that there will be no millennium. The struggle between Christ and His saints on the one hand and the wicked world and Satan on the other, is waged in the Church on earth; so the great Doctor describes it in his work De Civitate Dei. In the same book he gives us an allegorical explanation of Chapter 20 of the Apocalypse. The first resurrection, of which this chapter treats, he tells us, refers to the spiritual rebirth in baptism; the sabbath of one thousand years after the six thousand years of history is the whole of eternal life — or in other words, the number one thousand is intended to express perfection, and the last space of one thousand years must be understood as referring to the end of the world; at all events, the kingdom of Christ, of which the Apocalypse speaks, can only be applied to the Church (City of God XX.5-7). This explanation of the illustrious Doctor was adopted by succeeding Western theologians, and millenarianism in its earlier shape no longer received support.
The millenium was rejected for one and only one reason: the evil Rome (which was to have been destroyed) converted to chrstianity, and it could no longer play its role as the villain to be destroyed. Thus the “messiah” and the “messianic kingdom” were “spiritualized” beyond recognition, and (strangely) this is the one and only heresy which has never re-entered the Catholic Church because both Left and Right don’t want any messiah mucking things up for them.