I very much believe in the bible. One of my electives 50 years ago involved studying the Pentateuch. But some bible beliefs just happen to be wrong. I find many of the JW are in that category.
All scripture is ...beneficial. Of course it is---but much more so if you are reading it with the third person of the trinity, the Holy Spirit. Since you do not think He exists, that puts the JW interpretation of scripture at a distinct disadvantage.
Back up a few verses before Mark 7:13 in order to see what tradition is being referred to. Quoting 7:13 in this instance in reference to my comment that you think the bible is the only source of information about god is simply specious on your part.
My religion is the one that showed me where to find the pearl of great price. Which religion it is is should not be important to you. Why my religion has given me more than yours ever can should be of greater to concern to you.