9 Many then fell before the demon of the noon-day. Would ye know how many? He goes on, and says, “A thousand shall fall beside you, and ten thousand at your right hand; but it shall not come near you”. To whom, brethren, but to Christ Jesus, is this said?...For the members, the body, and the head, are not separate from one another: the body and the head are the Church and her Saviour. How then is it said, “A thousand shall fall beside you, and ten thousand by your right hand”?
Because they shall fall before the devil, that destroys at noon. It is a terrible thing, my brethren, to fall from beside Christ, from His right hand but how shall they fall from beside Him? Why the one beside Him, the other at His right hand? Why a thousand beside Him, ten thousand at His right hand? Why a thousand beside Him? Because a thousand are fewer than the ten thousand who shall fall at His right hand. Who these are will soon be clear in Christ's name; for to some He promised that they should judge with Him, namely, to the Apostles, who left all things, and followed Him....Those judges then are the heads of the Church, the perfect.
To such He said, “If you will be perfect, go and sell that you have, and give to the poor.” What means the expression, “if you will be perfect”? It means, if you will judge with Me, and not be judged....Many such at that period, who had distributed their all to the poor, and already promised themselves a seat beside Christ in judgment of the nations, failed amid their torments under the blazing fire of persecution, as before the demon of the noon-day, and denied Christ. These are they who have fallen “beside” Him: when about to sit with Christ for the judgment of the world, they fell.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)