So, if I'm hearing you...<quoted text>
Tradition is important. In Judaism we have customs and we have law. Both are considered tradition. Like I said, there are core components which have function, irrespective on their sources. No where in the law does it say one has to know Hebrew to be a Jew, but without Hebrew one can not fully engage in all the activities that make Judaism Judaism. Brit is an initiation ceremony. Thats what makes the people. How truthful, using Western standards, that the bible may be is irrelevant. Its done. It has a function.(and as far I as know it has benign consequences) You should watch Fiddler in the Roof.
And yes, Judaism is based on practice. And peoplehood. The only real canon is that God is one. Thats the core belief. The rest is commentary.
Different Jewish movements have different viewpoints about the authenticity of the Torah ranging from literal word of god to ...mans recollection or interpretation of what man thought God was saying.....But yet all the main movements believe in following (some semblance of) the tradition, regardless.
WHY we do it isn't important. "....irrespective on their sources.."
We don't have to believe in anything and we don't know who wrote all this down or why.
As in the Army "There's no reason for it, it's policy."
It's a habit, a tradition. We do it this way because we've always done it this way.
What does "God is one" mean to you?