John Gill Commentary Isaiah 28:24

"Doth he that ploweth to sow plow continually? doth he [continually] open and harrow his ground?" — Isaiah 28:24 (ASV)

Does the ploughman plough all day to sow? &c.] Or, "every day"; he ploughs in order to sow; by ploughing he prepares the ground for sowing, that is his end in ploughing; and he may plough a whole day together when he is at it, but he does not plough every day in the year; he has other work to do besides ploughing, as is later mentioned; such as breaking of clods, sowing seed, and threshing the grain after it is ripe, and reaped, and gathered.

The prophet signifies that the Lord, like a ploughman, had different sorts of work; he was not always doing one and the same thing; and particularly, that he would not be always admonishing and threatening men, and making preparation for his judgments, but in a little time he would execute them, signified by after metaphors:

Does he open and break the clods of his ground? He does, with a mallet or iron bar, or with the harrow; whereby the ground is made even, and so more fit for sowing.

The Targum interprets the whole in a mystical sense, of the instructions of the prophets, thus, "at all times the prophets prophesy to teach, if perhaps the ears of sinners may be opened to receive instruction;"

And it may be applied to the work of the Spirit of God upon men's hearts, by the ministry of the word: the heart of man is like the "fallow ground", hard and obdurate, barren and unfruitful; the ministry of the word is the "plough", and ministers are the "ploughmen"; but it is the Spirit of God that makes their ministrations useful, for the conviction of the mind, the pricking of the heart, and breaking it in pieces; see (Jeremiah 4:3) (23:29) .