In 1949, he advised Pope Pius XII to revise the Good Friday prayer, which previously contained offensive references to the Jews, to wit, the words "perfidious Jews."

He also noted that Catholics did not kneel when they prayed for the Jews on Good Friday, though they knelt for all the other petitions. Pope Pius modified the language (although only later did Pope John XXIII excise the negative language about the Jews altogether) and implemented a kneeling posture as Isaac had suggested.

He thus helped start the road that led to Vatican II's declaration Nostra aetate (1965), whose paragraph #4 represents a monumental shift in perspective towards the Jews in Roman Catholic thought.

https://en.wikipedia.org/wiki/Jules_Isaac