Therefore the Old Law should have been given to all nations, and not to one people only. (Aquinas: 811) Aquinas responds in these words:

Although the salvation, which was to come through Christ, was prepared for all nations, yet it was necessary that Christ should be born of one people, which, for this reason, was privileged above other peoples, according to Rom. ix. 4: To whom, namely, the Jews, belongeth the adoption as of children of God... And the testament, and the giving of the Law;... whose are the fathers, and of whom is Christ according to the flesh. (Aquinas: 813)

But while on the one hand, Aquinas tried to be sympathetic and tolerant, on the other, he created an undesirable duality when he refused to resist some stereotypical images of Jews as usurers and murderers of Christ. When he had the opportunity to dispel some old beliefs and add a new and refreshing angle to the age-old prejudice held against Jews, Aquinas failed miserably. In response to the objection that:

the Old Law mercifully forbade strangers to be molested; for it is written (Exod. xxii. 21): Thou shalt not molest a stranger, nor afflict him, for yourselves also were strangers in the land of Egypt; and (xxiii. 9): Thou shalt not molest a stranger, for you know the hearts of strangers, for you also were strangers in the land of Egypt. But it is an affliction to be burdened with usury. Therefore the Law unsuitably permitted them (Deut. xxiii. 19, 20) to lend money to strangers for usury. (Aquinas: 940)

What Aquinas said is definitely worth reading:

It was not the intention of the Law to sanction the acceptance of usury from strangers, but only to tolerate it because of the proneness of the Jews to avarice, and in order to promote an amicable feeling towards those out of whom they made a profit. (Aquinas: 942)

Aquinas thus had some fixed notions about Jews, just like many other thinkers and this created confusion among those who initially found him more tolerant on this subject. Upon closer exploration, it becomes clearer that duality on this issue arises not from Aquinas'...

This means that on the one hand, Aquinas wanted to present Jews in a better light but on the other, he also had to protect certain moral and ethical rules including objection to usury, killing and treachery. So while Jews may have been the chosen people for the Old Law in Aquinas' view, they were certainly not deserving of being the chosen ones when seen in the light of their unethical activities.
In this subject, we shall take help from some commentaries made on Aquinas's view of Jews as they would explain how duality destroyed Aquinas' tolerant stance. In the Catholic Historical Review author Edward Synan writes: "In the tradition of Aristotle, Brother Thomas produced reasoned condemnations of usury (one thinks of the intolerable 'servicing' of national debts in our time). Hood suggests a parallel with prostitution, an evil tolerable to avoid greater evils, as a way that Aquinas might have eased this ban. In the name of natural law Thomas explicitly defended the rights of Jewish parents over the upbringing of their children" (Synan, 550). Hood (1995) had earlier said that."..toleration of the Jews certainly did not flow logically from the theological vision embodied in canon law, which saw them as wicked..." (Hood, 110).

Thus while Aquinas' work may be remembered by many for its original thought, his arguments in the case of Jews lost their credibility because of frequent duality. On the one hand, we are told to accept Jews as deserving candidates for Old Law while on the other hand, Jews are shown in biased light when it comes to some ethical and moral rulings of Aquinas.

References

Aquinas, Thomas. Basic Writings of Saint Thomas Aquinas. Volume: 2. Anton C. Pegis (Ed.) Hackett Publishing. Indianapolis, in. 1997.

John Y.B. Hood, Aquinas and the Jews (U. Of Pennsylvania, 1995)

Edward a. Synan, review of Kenneth R. Stow, Alienated Minority. The Jews of Medieval Latin Europe in the Catholic Historical Review, Vol. 80, No. 1 (January 1994)