John Gill's Exposition of the Whole Bible
Isaiah 41:15
Behold, I will make thee a new sharp threshing instrument, having teeth,.... The Vulgate Latin version renders it, "as a new threshing cart, having teeth like saws"; and the Septuagint and Arabic versions, "as the new threshing wheels of a cart, in the manner of saws"; for corn with the Jews was threshed out by drawing a cart with wheels over it, which wheels were stuck with teeth or spikes of iron; see Isaiah 28:27, or by a cart or sledge filled with stones to press it down, and at the bottom with iron teeth, which being drawn to and fro by oxen over the sheaves, separated the grain from the husk. Beckius has given a figure of this instrument t, and some such like instrument is still made use of in the eastern countries, as Monsieur Thevenot u relates;
"at Damascus (he says), and almost all Turkey over, they thresh not the corn, but after it is cut down they put it up in heaps, and round the heaps they spread some of it four or five feet broad, and two feet thick; this being done, they have a kind of sled, made of four pieces of timber in square, two of which serve for an axle tree to two great rollers, whose ends enter into these two pieces of timber, so as that they easily turn in them: round each of these rollers, there are three iron pinions, about half a foot thick, and a foot in diameter, whose pinions are full of teeth, like so many saws: there is a seat placed upon the two chief pieces of the timber, where a man sits, and drives the horses, that draw the machine, round about the lay of corn that is two foot thick; and that cutting the straw very small, makes the corn come out of the ears without breaking it, for it slides betwixt the teeth of the iron: when the straw is well cut, they put in more, and then separate the corn from that bashed straw, by tossing all up together in the air with a wooden shovel; for the wind blows the straw a little aside, and the corn alone falls straight down--in some places that machine is different, as I have seen (adds he), in Mesopotamia; where, instead of those pinions round the rollers, they have many pegs of iron, about six inches long, and three broad, almost in the shape of wedges, but somewhat broader below than above, fastened without any order into the rollers, some straight, and others crossways; and this engine is covered with boards over the irons, whereon he that drives the horse sits--they take the same course in Persia.''
Some apply this to the apostles of Christ, compared to oxen that tread out the corn; and who not only ploughed and sowed, but threshed in hope, and were instruments of bringing down every "high thing", comparable to mountains and hills, "that exalted itself against the knowledge of God", and of reducing it "to the obedience of Christ"; see 1 Corinthians 9:9, but it seems rather to refer to Constantine, a Christian emperor, brought forth and brought up in the church; the same with the man child the woman brought forth, caught up into heaven, raised to the Roman empire, and who ruled the nations, the Pagan ones, with a rod of iron, Revelation 12:5 and then the church, who before was but as a worm, weak and contemptible, now became powerful and formidable; and therefore compared to a new threshing instrument, heavy, sharp, and cutting:
thou shall thresh the mountains, and beat them small, and shalt make the hills as chaff; which metaphorically design kingdoms and states; so the Targum,
"thou shalt slay the people, and consume kingdoms"; so Jarchi and Kimchi interpret it of kings and princes; and Aben Ezra particularly of the Babylonians; but these were not destroyed by the people of God, but by the Persians: it is better therefore to understand it of the Roman emperors, and of the Roman empire conquered by Constantine, and destroyed as Pagan, and when every mountain and island were moved out of their places, Revelation 12:7, and the prophecy may have a further accomplishment in the destruction of Rome Papal, and all the antichristian states, when the kingdom and interest of Christ, signified by a stone cut out without hands, shall break in pieces, and consume all other kingdoms: which shall become like the chaff of summer threshing floors, and the wind shall carry them away, and no place be found for them, as follows; see Daniel 2:34, this threshing of the nations is ascribed to the church, though only as an instrument, the work is the Lord's, as in Isaiah 41:20.
t Beckius, notes on the Targum on 1 Chron. xx. 3. p. 210. u Travels, Part 2. B. 1. c. 5. p. 24.