Martin Luther held to some very anti semitic beliefs I believe.
It was a pique. Luther had made the "mistake" of studying the Bible and realized the importance of the Jewish people. Meanwhile, he was getting no support from the Catholic hierarchy for the reforms he thought that mandated. So he approached the rabbis to gain assistance with his radical ideology and they, out of their habituated suspicion of Christians, turned him down.
Luther never forgave them. What was that thingy Christ taught about that?