Albert Barnes on Matthew 24:41

Two women, etc. Grinding in the East was performed, as it is now, chiefly by hand. The mill-stones were about two feet in diameter, and half a foot in thickness. The lower one was fixed, and the upper one was turned by a handle, or crank. This was done by two persons, who sat opposite to each other. One took hold of the mill-handle, and turned it half way round; the other then seized it, and completed the revolution. This was done by women; by servants of the lowest order; and was a very laborious employment. See Ex 11:5 Job 31:10, Isa 47:2, Jud 16:21. The meaning of this verse is similar to the former, of two persons sitting near to each other, one shall be taken, and the other left. The calamity would be sudden, and would come upon them before they were aware.