For before the harvest, when the blossom is gone and the flower becomes a ripening grape, He will cut off the shoots with a pruning knife and remove and discard the branches.
5. For when the harvest shall be at hand. Literally it is, “in presence of the harvest;” but we must soften the harshness of the expressions; and it cannot be doubted that the meaning of the Prophet is, that when the harvest is close at hand, and when the grapes are nearly ripe, the whole produce, in the expectation of which wicked men had rejoiced...
Interpreters are very much at a loss where to find this land that lies beyond the rivers of Cush. Some take it to be Egypt, a maritime country, and full of rivers, and which courted Israel to depend upon them, but proved broken reeds; but against this it is strongly objected that the next chapter is distinguished from this by the title of the burden of Egypt.
Commenting on Isaiah 18:1-7
For afore the harvest,.... Or vintage: the above metaphor is carried on; before the designs and schemes of the people above described are ripe for execution, who promised themselves a large harvest of their neighbours: when the bud is perfect; when the bud of the vine is become a perfect grape, though unripe; when the scheme was fully laid, and with perfect and consummate wisdom...