Martin Luther: The Jews and Their Lies
(extracts)
I had made up my mind to write no more either about the Jews or against them. But since I learned that these miserable and accursed people do not cease to lure to themselves even us, that is, the Christians, I have published this little book, so that I might be found among those who opposed such poisonous activities of the Jews who warned the Christians to be on their guard against them. I would not have believed that a Christian could be duped by the Jews into taking their exile and wretchedness upon himself. However, the devil is the god of the world, and wherever God's word is absent he has an easy task, not only with the weak but also with the strong. May God help us. Amen.
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He did not call them Abraham's children, but a "brood of vipers"
. Oh, that was too insulting for the noble blood and race of Israel, and they declared, "He has a demon' . Our Lord also calls them a "brood of vipers"; furthermore in John 8 <:39,44> he states: "If you were Abraham's children ye would do what Abraham did.... You are of your father the devil. It was intolerable to them to hear that they were not Abraham's but the devil's children, nor can they bear to hear this today.
http://www.jewishvirtuallibrary.org/jsource/anti-semitism/Luther_on_Jews.html