Jamieson, Fausset and Brown on Isaiah 28:23

23. Calling attention to the following illustration from husbandry (Psa 49:1, 2). As the husbandman does his different kinds of work, each in its right time and due proportion, so God adapts His measures to the varying exigencies of the several cases: now mercy, now judgments; now punishing sooner, now later (an answer to the scoff that His judgments, being put off so long, would never come at all, Is 5:19); His object being not to destroy His people any more than the farmer's object in threshing is to destroy his crop; this vindicates God's "strange work" (Is 28:21) in punishing His people. Compare the same image, Jr 24:6; Ho 2:23; Mt 3:12.