Shall beat off; or, shall beat out; which is not meant in a way of punishment, which is rather designed by threshing, as Isaiah 21:10, Isaiah 25:10, than by beating; but as an act of mercy, as is evident from the following clause of this, and from the next verse. It is a metaphor from some grains which were beaten out with a rod or staff, of which see Isaiah 28:27,28, and then were carefully gathered and laid up, for the use of man. From the channel of the river unto the stream of Egypt; from Euphrates to Nilus, which were the two borders of the Land of Promise, Joshua 1:4, Joshua 13:3. All the Israelites which are left in the land; which are here opposed to those of them that are dispersed into foreign parts, such as Assyria and Egypt. Ye shall be gathered one by one; which signifies either the smallness of the remnant of that numerous people; or rather God's exact and singular care of them, that not one of them should be lost.
Related Commentaries of Isaiah 27:12
Isaiah 27:12
12 And it shall come to pass in that day, that the LORD shall beat off from the channel of the river unto the stream of Egypt, and ye shall be gathered one by one, O ye children of Israel.