37 And as in the days of Noe, so shall also the coming of the Son of man be. 38 For as in the days before the flood, they were eating and drinking, marrying and giving in marriage, even till that day in which Noe entered into the ark, 39 And they knew not till the flood came, and took them all away; so also shall the coming of the Son of man be. 40 Then two shall be in the field: one shall be taken, and one shall be left. 41 Two women shall be grinding at the mill: one shall be taken, and one shall be left.
Hilary: The two in the field, are the two people of believers and unbelievers, whom the day of the Lord shall overtake, as it were in the labours of this life. And they shall be separated, one being taken and the other left; this shews the separation that shall be between believers and unbelievers; when God’s wrath is kindled, the saints shall be gathered into His garner, and the unbelievers shall be left as fuel for the fire from heaven. The same is the account to be given of that, “Two shall be grinding at the mill.” The mill is the work of the Law, but as some of the Jews believed through the Apostles, so some shall believe through Elias, and be justified through faith; and one part shall be taken through this same faith of good works, the other part shall be left unfruitful in the work of the Law, grinding in vain, and never to produce the bread of heavenly food.
Jerome: “Two men in one field” shall be found performing the same labour, sowing corn together, but not reaping the same fruit of their labour. The two “grinding together” we may understand either of the Synagogue and the Church, which seem to grind together in the Law, and to make of the same Scriptures meal of the commandments of God; or of other heresies, which out of both or one Testament, seem to grind meal of their own doctrines.
Remigius: These words denote three orders in the Church. “The two men in the field” denote the order of preachers, to whom is committed the field of the Church; by “the two grinding at the mill,” the order of the married priests, who while with a divided heart they are called first to one side, then to the other, do, as it were, ever turn round a mill. . . . But in all these orders are good and bad, righteous and unrighteous, so that some shall be taken, and some left.
Origen: The body is laid as sick on the bed of carnal passions, the soul grinds in the mill of this world, and the bodily senses labour in the field of the world.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. I (London: Rivington, 1842).