Isaiah uses harvest images to describe the enemy's fate. In the month of May, the vines were pruned to remove the infertile shoots. This happened after the grain harvest and before the fruit harvest, when the new grapes were beginning to grow. Pruning helped to ensure a good harvest.
The enemy nation would experience the judgment of the Lord. They would be removed just like the bad shoots from the vine and become like food for the wild animals and birds.
The mention of summer
and winter
indicates that this state of affairs would last for a long time.
5 For before the harvest, when the blossom is over, and the flower becomes a ripening grape, he cuts off the shoots with pruning hooks, and the spreading branches he lops off and clears away.