You’re doing just great, actually. As I’ve mentioned before some people won’t attempt to try to see things from a different perspective and therefore give up trying to learn about something new altogether.
Correct me if I am wrong but most Evangelical subscribe to a theology that basically holds that “true” religion is based on what is written in the inspired Scriptures. The Bible is the authority, and what is believed is usually based and sometimes limited to what is inscribed therein. This is like a “cart before the horse” scenario that can cause one to ask questions that don’t actually apply.
To illustrate: Judaism, like Catholicism, was already a functioning system of worship with faithful members and a liturgy before and during the production of their Scripture texts and their collection or canonizations. Abraham did not have a Bible to base his religion on. He had an ongoing theophany, one which the entire nation of Israel ended up having through Moses at the foot of Mount Sinai. Their religion came first, and faithful followers of that religion composed their Scriptures.
Orthodox Christians and Catholics hold a similar view of Christianity. Their religion, while including a strong faith in the Hebrew Scriptures, was based on what they believed was an epiphany. The texts that later became the New Testament are a reflection of Christianity, not its basis, which was a Jesus of Nazareth. By the time the epistles and gospels were composed the movement already was on its way, and a functioning liturgy and creeds existed for a century before the question of canonization of these texts even arose.
While not arguing the validity of the Evangelical or Fundamentalist stand, at least for Jews and Catholics the Scriptures are a product of the religious systems that produced them, indivisible from the practices and traditions that formed them.
That being case, one doesn’t ask what authority holy writ has on a given subject in Judaism. Jews accept holy writ because it comes from the religion revealed to them from Heaven. The religion itself is “inspired,” to use the Christian term, therefore its message, which includes holy writ, is generally accepted as inviolate.
Were one to require that the texts of Judaism be subjected to the demands of some sola scriptura-believing Christians would also demand that Judaism be incapable of existing in any true form until all its Scriptural texts were composed. This would not be possible for without the Jews to write them there would be no Scriptures to begin with.
True religion cannot be based on the Scriptures alone for the Scriptures would not have been composed without the truth being practiced to begin with.