O my threshing - "O thou, the object upon which I shall exercise the severity of my discipline; that shalt lie under my afflicting hand, like corn spread upon the floor to be threshed out and winnowed, to separate the chaff from the wheat!" The image of threshing is frequently used by the Hebrew poets, with great elegance and force, to express the punishment of the wicked and the trial of the good, or the utter dispersion and destruction of God's enemies. Of the different ways of threshing in use among the Hebrews, and the manner of performing them, see the note on Isaiah 28:27; (note).
Our translators have taken the liberty of using the word threshing in a passive sense, to express the object or matter that is threshed; in which I have followed them, not being able to express it more properly, without departing too much from the form and letter of the original. "Son of my floor," Hebrews It is an idiom of the Hebrew language to call the effect, the object, the adjunct, any thing that belongs in almost any way to another, the son of it. "O my threshing." The prophet abruptly breaks off the speech of God; and instead of continuing it in the form in which he had begun, and in the person of God, "This I declare unto you by my prophet," he changes the form of address, and adds, in his own person, "This I declare unto you from God."
O my threshing - The words ‹to thresh,‘ ‹to tread down,‘ etc., are often used in the Scriptures to denote punishments inflicted on the enemies of God. An expression likes this occurs in Jeremiah 51:33, in describing the destruction of Babylon: ‹The daughter of Babylon is like a threshing floor; it is time to thresh her.‘ In regard to the mode of threshing among the Hebrews, and the pertinency of this image to the destruction of the enemies of God, see the note at Isaiah 28:27. Lowth, together with many others, refers this to Babylon, and regards it as an address of God to Babylon in the midst of her punishment: ‹O thou, the object on which I shall exercise the severity of my discipline; that shall lie under my afflicting hand like grain spread out upon the floor to be threshed out and winnowed, to separate the chaff from the wheat.‘ But the expression can be applied with more propriety to the Jews; and may be regarded as the language of “tenderness” addressed by God through the prophet to his people when they should be oppressed and broken down in Babylon: ‹O thou, my people, who hast been afflicted and crushed; who hast been under my chastening hand, and reduced to these calamities on account of your sins; hear what God has spoken respecting the destruction of Babylon, and your consequent certain deliverance.‘ Thus it is the language of consolation; and is designed, like the prophecies in Matthew 1:1).
That which I have heard - This shows the scope or design of the whole prophecy - to declare to the Jews the destruction that would come upon Babylon, and their own consequent deliverance. It was important that they should be “assured” of that deliverance, and hence, Isaiah “repeats” his predictions, and minutely states the manner in which their rescue would be accomplished.