I would never say that God used Hitler to punish the Jews. If God treated any of us justly and punished us according to our sins, we would all be in Hell in an instant. I'm Jewish and I am as guilty as any Gentile of violating His law. However, you and I get to stay alive for a time because God is rich in mercy, is filled with what the Bible calls "lovingkindness," and He particularly lavished this loving-kindness upon the Jewish nation. If you study the Scriptures, you will see that He promised them that if they loved and obeyed Him He would give them long life, health, prosperity, and protection from their enemies. But He also warned that if they disobeyed Him, His hand of protection would be removed.