Doctrine of Jewish Witness
One book that had a critical influence on the fate of Judaists in the past is said to be The City of God written by Augustine in the fifth century:
De Civitate Dei (full title: De Civitate Dei contra Paganos, translated in English as The City of God Against the Pagans) or The City of God is a book of Christian philosophy written in Latin by Augustine of Hippo in the early 5th century AD. The book was in response to allegations that Christianity brought about the decline of Rome and is considered one of Augustine's most important works, standing alongside The Confessions, The Enchiridion, On Christian Doctrine, and On the Trinity. As a work of one of the most influential Church Fathers, The City of God is a cornerstone of Western thought, expounding on many profound questions of theology, such as the suffering of the righteous, the existence of evil, the conflict between free will and divine omniscience, and the doctrine of original sin.In this book, the greatest scholar of the era Augustine mentioned Judaists in a kind of very sarcastic and hostile manner. He claimed that Judaists should not be killed but allowed to live as a kind of witnesses of the glorious emergence of Christ Jesus. As long as Judaists lived with the Old Testament, they would contribute to Christianity prevailing in pagan communities and every region in and around the Roman Empire, Augustine stressed. According to Augustine, the Vatican should make the best use of existence of Judaists in its mission to convert heathens and pagans into Christianity by presenting Judaists as living evidence for the historical event of Christ Jesus' mission around Jerusalem in the first century.
http://en.wikipedia.org/wiki/City_of_God_(book)
St. Augustine
City of God
But the Jews who slew Him, and would not believe in Him, because it behoved Him to die and rise again, were yet more miserably wasted by the Romans, and utterly rooted out from their kingdom, where aliens had already ruled over them, and were dispersed through the lands (so that indeed there is no place where they are not), and are thus by their own Scriptures a testimony to us that we have not forged the prophecies about Christ. And very many of them, considering this, even before His passion, but chiefly after His resurrection, believed on Him, of whom it was predicted, "Though the number of the children of Israel be as the sand of the sea, the remnant shall be saved." [Isaiah 10:22 and Romans 9:27-28] But the rest are blinded, of whom it was predicted, "Let their table be made before them a trap, and a retribution, and a stumbling-block. Let their eyes be darkened lest they see, and bow down their back alway." [Psalm 69:22-23 and Romans 9:9-10] Therefore, when they do not believe our Scriptures, their own, which they blindly read, are fulfilled in them, lest perchance any one should say that the Christians have forged these prophecies about Christ which are quoted under the name of the sibyl, or of others, if such there be, who do not belong to the Jewish people. For us, indeed, those suffice which are quoted from the books of our enemies, to whom we make our acknowledgment, on account of this testimony which, in spite of themselves, they contribute by their possession of these books, while they themselves are dispersed among all nations, wherever the Church of Christ is spread abroad. For a prophecy about this thing was sent before in the Psalms, which they also read, where it is written, "My God, His mercy shall prevent me. My God hath shown me concerning mine enemies, that Thou shalt not slay them, lest they should at last forget Thy law: disperse them in Thy might."[Psalm 69:10-11] Therefore God has shown the Church in her enemies the Jews the grace of His compassion, since, as saith the apostle, "their offence is the salvation of the Gentiles."[Romans 11:11] And therefore He has not slain them, that is, He has not let the knowledge that they are Jews be lost in them, although they have been conquered by the Romans, lest they should forget the law of God, and their testimony should be of no avail in this matter of which we treat. But it was not enough that he should say, "Slay them not, lest they should at last forget Thy law," unless he had also added, "Disperse them;" because if they had only been in their own land with that testimony of the Scriptures, and not every where, certainly the Church which is everywhere could not have had them as witnesses among all nations to the prophecies which were sent before concerning Christ.
http://people.bu.edu/dklepper/RN470/augustine_jews.html
Unwilling Witnesses: St. Augustine and the Witness Doctrine
St. Augustine’s writing on Judaism was remarkably nuanced, deepening over the course of 30 years as his thoughts on scripture developed. His most lasting contribution to the topic was his “doctrine of Jewish witness,” often simply called “the witness doctrine,” which viewed the Jews not solely as “Christ-killers” to be condemned, but as a vital ingredient in the spread of Christianity. The doctrine came to be accepted by the Church, and informed subsequent order of protection by the Church for the lives of Jewish people.
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According to Augustine, this is part of God’s inscrutable justice: to make the Jews deaf and blind, for a time, so that the Gospel could spread.[34] "God's hardening of Israel was strategic, not punitive. And it was only temporary. As history rushes to its conclusion, and as the ‘full number’ of Gentiles comes to Christ, God will cease hardening 'part of Israel. . . . And so all Israel will be saved' (Romans 11:26). In the end, God has mercy on all (Romans 11:32)."
There is dense layering of typology in all of this, out of which Augustine builds his unique image of the Jews. They are Cain the wanderer and fratricide, marked by their distinctly Jewish appearance and praxis and known for the “murder” of their brother, Jesus. Their “slavery” to the church comes from Noah’s curse of Ham, thus condemning them to “witness” to Christian truth by carrying the books that underlie the Gospel. The books themselves are the scripture, which are fulfilled in Christ and which they read without understanding.
http://www.patheos.com/blogs/godandthemachine/2013/08/st-augustine-and-the-jews/
If the Vatican still holds this theory as one of its leading principles, Judaists cannot be safe at all living in Europe and any other regions where the Vatican has an influence on people's minds and hearts.
It is even possible that the Vatican just though that the God was using Judaists in a special manner to further spread and deepen Christianity by handing them to Hitler and Nazis when millions of Europeans Judaists were being executed during and before WWII.
However, in reference to the above quotation, Augustine seems to have believed that God should stop using Judaists as a means to spread Christianity when the world is filled with Christians. Augustine thought that Judaists would be also saved by God eventually. Nonetheless, the doctrine of Jewish witness seems to have been too influential in the Catholic world. Especially, it is God that saves Judaists in the final stage of history but not the Vatican or Christians. The Vatican can make an excuse for not saving poor Judaiats at any time.
But, it is a dangerous to blindly accept the doctrine of Jewish witness. In fact, after the death of Augustine, God gave Islam to Arabs. It is an act that is completely unnecessary in the paradigm of Christianity and the Vatican. Could Augustine, if he had long lived to see the emergence of Islam, assure himself that God used Christianity in order to make it an underlying condition for establishing Islam? Could Augustine accept the "doctrine of Christian witness?"
The correct answer must be that God uses Judaism, Christianity, and Islam only to show His omnipotence to mankind. If Judaists cannot show good examples to the world, God would send His Son as Christ or the Messiah to the world. If Christians cannot show good examples to Arabs and so on, he would give Islam to some tribes. But, it is enough. And the Last Judgment should fall on mankind. This scenario sounds holier and more reasonable.
Yet, we can find one of the most influential doctrines against Judaists in Augustine's works. So, we may need another doctrine to save everybody.
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Luk 9:14 For they were about five thousand men. And he said to his disciples, Make them sit down by fifties in a company.
Luk 9:15 And they did so, and made them all sit down.
Luk 9:16 Then he took the five loaves and the two fishes, and looking up to heaven, he blessed them, and brake, and gave to the disciples to set before the multitude.