Religion would be the major factor in this case, being catholicism and judaism faiths that have very different basic beliefs. As an example, they differ the understanding of who Jesus is. Judaism sees Jesus as a Jew, a devout practicing Jew who went to the temple, prayed the psalms a was a respected Jewish leader. But catholics believe that Jesus was the son of God, the Messiah that the old testament prophets had predicted would come one day to save us from our sins. Judaism does not believe that Jesus was the Messiah, and are still waiting for him, they recognize Jesus as a very holy Jew, a great Jewish prophet, but reject the idea they he was the Messiah.