John Calvin Commentary Isaiah 63:2

"Wherefore art thou red in thine apparel, and thy garments like him that treadeth in the winevat?" — Isaiah 63:2 (ASV)

Why are your garments red? He proceeds with the same subject. However, since it would have diminished the force of the narrative, he does not immediately explain from where the red color of God’s garments came. Instead, he continues to ask questions to arouse their minds to consider what is strange and uncommon.

He means that this sprinkling of blood is something remarkable and extraordinary. The comparison drawn from a "wine-press" is highly appropriate; for the town Bozrah, which he mentioned a little before, lay in a vine-bearing district. As if he had said, "There will be other vintages than those which are customary, for blood shall be shed instead of the juice of the grapes."