Albert Barnes Commentary Isaiah 18:5

"For before the harvest, when the blossom is over, and the flower becometh a ripening grape, he will cut off the sprigs with pruning-hooks, and the spreading branches will he take away [and] cut down." — Isaiah 18:5 (ASV)

For before the harvest - This verse is evidently figurative, and the image is drawn from what began in the previous verse. There, God is represented as calmly observing the plans of the people referred to here—as the sun shines serenely on the herb, or the dew falls on the grass.

That figure supposes that they had formed plans and that they were advancing to maturity, like a growing harvest, while God surveyed them without intervention. This verse continues the figure and affirms that those plans shall not be mature; and that God will intervene and defeat them while they are maturing—as if a man should enter the harvest field and cut it down after it had been sown, or go into the vineyard and cut down the vines while the green grape was beginning to ripen.

It is, therefore, a most beautiful and expressive figure, intimating that all their plans would be foiled even when they had the prospect of a certain accomplishment.

When the bud is perfect - The word bud here (פרח perach) denotes either a blossom, or a sprout, shoot, or branch. Here it denotes probably the blossom of the grain; or it may be the grain when it is set. Its meaning is, when their plans are maturing, and there is every human prospect that they will be successful.

And the sour grape is ripening - Begins to turn, or is becoming mature.

In the flower - (נצה n^etsâh). The blossom. This should be read rather, ‘and the flower is becoming a ripening grape.’ The common version does not make sense, but with this translation the idea is clear. The sense is the same as in the former phrase—when their plans are maturing.

He shall cut off the sprigs - These are the shoots, the small limbs on which the grape is hanging. It is as if a man should enter a vineyard and, while the grape is ripening, not only cut off the grape but also the small branches that bore it, thus preventing it from bearing again. The idea is, not only that God would disconcert their present plans, but that He would prevent them from forming any in the future. Before their plans were matured, and they obtained the anticipated triumph, He would effectually prevent them from forming such plans again.