Jamieson, Fausset and Brown on Isaiah 63:2

2. The prophet asks why His garments are "dyed" and "red."

winefat--rather, the "wine-press," wherein the grapes were trodden with the feet; the juice would stain the garment of him who trod them (Re 14:19, 20; 19:15). The image was appropriate, as the country round Bozrah abounded in grapes. This final blow inflicted by Messiah and His armies (Re 19:13-15) shall decide His claim to the kingdoms usurped by Satan, and by the "beast," to whom Satan delegates his power. It will be a day of judgment to the hostile Gentiles, as His first coming was a day of judgment to the unbelieving Jews.