24 When the Son of Man, He says, shall come in His glory, and all the Angels with Him. Behold, O man, before what multitudes you shall come to judgment. Every race of mankind will then be present. Reckon, therefore, how many are the Roman nation; reckon how many the barbarian tribes now living, and how many have died within the last hundred years; reckon how many nations have been buried during the last thousand years; reckon all from Adam to this day.
Great indeed is the multitude; but yet it is little, for the Angels are many more. They are the ninety and nine sheep, but mankind is the single one. For according to the extent of universal space, must we reckon the number of its inhabitants. The whole earth is but as a point in the midst of the one heaven, and yet contains so great a multitude; what a multitude must the heaven which encircles it contain? And must not the heaven of heavens contain unimaginable numbers?
And it is written, Thousand thousands ministered unto Him, and ten thousand times ten thousand stood before Him; not that the multitude is only so great, but because the Prophet could not express more than these. So there will be present at the judgment in that day, God, the Father of all, Jesus Christ being seated with Him, and the Holy Ghost present with Them; and an angel's trumpet shall summon us all to bring our deeds with us. Ought we not then from this time forth to be sore troubled? Think it not a slight doom, O man, even apart from punishment, to be condemned in the presence of so many. Shall we not choose rather to die many deaths, than be condemned by friends?
Source: Catechetical Lectures (New Advent)