Isaiah 51:22

The God offering Israel a comforting promise was her master, Yahweh, the God of the covenant, the God who had taken her to Himself, who consistently defends His people. He promised that the Israelites would never again experience the outpouring of His wrath as they had. Obviously the Jews have experienced worse persecution in recent history than they did during the Babylonian exile: the German holocaust, the Russian pogroms, etc. And they will undergo the worst trials of their history in the Tribulation (cf. Jeremiah 30:4-7). I take it that God meant that He would not punish them as He had because He would provide the Servant to drink the cup of His wrath for His people. They would not have to suffer in the future as they had in the past because God would provide a Savior who would suffer in their place. That so many of the Jews have suffered terribly and will yet do so is because they have rejected the Savior that God provided.