OK let me try. To start with the words “old testament” are an insult.
So, if you are serious about your question, it needs to be refined. Do you want me to tell you what the author of Deuteronomy meant? Do you what me to tell you who I think that was? Do you want me to tell you what most Jews think or just what I think?
To start of with we do not celebrate mass murders as your “old testament” suggests. Your religion, not ours, celebrates the massacres described when the mythic early Jews invaded Canaan.
What you seem not to understand is that Judaism is not a precursor of Christianity nor it is a form of Christianity. We are a people that has roots at least 300 and perhaps 10000 years deep. The texts Christianity appropriated are uninterpretable to Jews in the form used by Christians.
You chose a text from the Torah. The Torah is much more then a part of your old testament. The understanding of the Torah comes from centuries of reading and interpretation These tests, are called Mishnah and Talmud. reflect rabbinic discussions that not just the literal words in the Torah but knowledge of Jewish traditions, “the oral Torah,” as well as ideas influenced by other philosophies and by science.
Beyond rabbinic tradition we have had wonderful scholars who have added to that tradition with ideas rooted in the enlightenment, science and tradition as divers as Buddhism and Kabbalah. And yes many of these scholars were also rabbis.
So try your question again, just tell me why you ask it?
Just the fact that you suggest some Jews and particularly rabbis recognize that parts of the torah are even mythical in nature throws a lot of Christian’s for a loop. After all it is all supposed to be the inspired word of God. never mind that one whole old testament book manages to not mention through whole chapters. And that the Book of Job is clearly a work of fiction based on an earlier story. Yes Christians who do not have to follow the law and are free from it spend an awful lot of time mired in the old testament.
There is little archeology evidence supporting the mass murders in Canaan or the invasion of Canaan. There is virtually no evidence of a mass Exodus from Egypt. Leaving open the possibility of just Moses and a few followers escaping Egypt while the story is really good, it maybe just that a story. Yet it’s the soul of the Jewish people. Of course the fact that every Passover the youngest at the table asks a chicken or the egg story about Passover is not known to many Christians or well gentiles. Of course the fact the Bible or Torah was written just as Hebrew was becoming a written language overlapping with when the Jewish people were enslaved by Assyria and Babylon goes without much notice.
The fact the Torah reflects the traditions of the Kings house at that time and those oral traditions more than the oral traditions of the common folks is rather unknown, and then there are the different traditions of Judah and Israel.
Does it really matter why he asks it. While you may not consider yourself a Rabbi in the most expansive definition of Rabbi you could be one, if you engage in the conversation. That is of course your choice. Even the child who asks why is there a Passover deserves an answer or at least a story.
I ca not answer it because I do not understand his question. I know Loo. His question is well intended but it isbased on so many flase assumptions that it can nto be answered.