John Calvin 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 when the harvest shall be at hand. Literally, this means “in the presence of the harvest.” However, we must soften the harshness of these expressions. It cannot be doubted that the Prophet’s meaning is this: when the harvest is close at hand, and when the grapes are nearly ripe, the entire produce, which wicked men had joyfully expected, will suddenly be snatched from them.

The Prophet continues on the same subject and, through these metaphors, confirms what he had previously stated: the wicked are not immediately cut off but flourish for a time, and the Lord spares them. However, when the harvest is near, when the vines put forth their buds and blossoms so that the sour grapes appear, the branches themselves will be cut down.

Thus, when the wicked are nearly ripe, not only will they be deprived of their fruit, but they and their offspring will also be rooted out. This is the end the Lord will bring upon the wicked, after permitting them to enjoy prosperity for a time. For they will be rooted out so that they cannot revive or spring up again in any way.

From this, we receive this great consolation: when God conceals Himself, He tests our faith and does not allow everything to be carried along by the blind violence of fortune, as pagans imagine. For God is in heaven, as if in His tabernacle, dwelling in His Church as if in a humble habitation; but at the proper time, He will come forth.

Let us, therefore, examine our consciences and ponder everything, so that we may sustain our minds with a promise like this, which alone will enable us to overcome and subdue temptations. Let us also consider that the Lord declares that He furthers the happiness of wicked men, which serves to display God’s mercy all the more illustriously.

If He instantly cut them down and took them away like a sprouting blade of grain, His power would not be so evident, nor would His goodness be so fully recognized, as when He permits them to grow to a great height, to swell and blossom, so that they may afterwards fall by their own weight; or as when, like large and full ears of grain, He cuts them down with pruning knives.