none2 > who gave the rabbinim the right to interpret whether something is literal or symbolic how do _they_ know
the answer is in your nearest copy of a Talmud. Learn the story of Shimon Amsuni (Kiddushin 57): he had a theory that every “es” in the Torah means something to add: “es hashamayim ve es haaertz” – Hashem created other things together with heavens and earth. So, he published much until he came up to “yiras es Hashem” – and concluded that you can’t be afraid in anything in addition to being afraid of Hashem – and he rejected the theory that he worked on for some years. This is the rigor of Talmudic analysis. When you look at different sugyous – sometimes, you can easily see the process. Sometimes, it is not that clear and the analysis might be simply justifying existing practice, but at least you’ll appreciate where these came from. Development of this technical approach is the major achievement of Babylonian Talmud specifically, as they were living “in the dark” missing a lot of information comparing with scholars in EY.