Replacement Theology:
Christian theology accepts the Hebrew Bible. It does not quarrel with the statements therein that the Jews were a special people chosen by God to receive the Torah and bring holiness into the world. But Christian theology says that the Jews failed in their mission. This is why God sent His “son” (Jesus) to straighten things out, but the Jews refused to recognize him as “god.”
As a result, God abandoned the Jews and replaced them with the “new chosen people”—the Christians. (Hence, the Christian segment of the Bible is called the “New Testament” which is Greek for “scripture.”)
By this line of reasoning however, there would no longer be any purpose for Jews in the world. They should disappear, like did so many mightier peoples. But by the first millennium—already 1,000 years after the death of Jesus—the Jews were still all over the place.
Christian theology had to come up with some sort of answer to this problem and it did. The Jews must have been doomed to wander the earth by God as a “witness people”—teste veritatis in Latin. The purpose of a witness people is to survive throughout history to bear witness at the end of days that Jesus is the Messiah, when he appears again for the so-called “Second Coming.”
But the explanations of Christian theology could not remove the sore spot that the presence—at times, strong and prosperous presence—of the Jews represented. At the heart of the matter was the Christian view of Judaism as a direct competitor for the soul of humanity.
The hostility that the Christians felt toward the Jews can be seen readily from the writings of the early fathers of the Christian Church. (See What Did They Think of the Jews? by Allan Gould, pp. 24-25.)
From John Chrysostom, the Patriarch of Constantinople, we get this:
“Jews are the most worthless of men - they are lecherous, greedy, rapacious - they are perfidious murderers of Christians, they worship the devil, their religion is a sickness ... The Jews are the odious assassins of Christ and for killing god there is no expiation, no indulgence, no pardon. Christians may never cease vengeance. The Jews must live in servitude forever. It is incumbent on all Christians to hate the Jews.”
From Gregory of Nyssa, we get more of the same:
“Slayers of the lord, murderers of the prophets, adversaries of god, haters of god, men who show contempt for the law, foes of grace, enemies of the father’s faith, advocates of the devil, brood of vipers, slanderers, scoffers, men whose minds are in darkness, leaven of the Pharisees, assembly of demons, sinners, wicked men, stoners and haters of righteousness.”
In some places, such calumny incited people to violence.
(We saw in Part 45, for example, how the Crusader mobs devastated the Jewish population of Europe, slaughtering 30%-50% of the Jews living there. Some 10,000 Jews of an estimated population of about 20,000-30,000 were murdered in 1095 as the first Crusade got under way.)
In other places, such calumny bred other forms of persecution.
http://www.simpletoremember.com/articles/a/blood_libel/