Source of sage rulings

Last time I asked you a question and you wrote that it was incomprehensible, so I will try to explain. The law of the muktaza and the law of the eruvin are renewed laws "invented" by the sages. In the 63 tractates that we have, there is Torah knowledge. There must be a divine source for this knowledge, so in the Torah's laws and commandments, the source of the knowledge that emanates from them and the depth in which they are is from the Torah itself. But a renewed law like the muktaza or washing of hands, where did the sages derive the wisdom and knowledge and the halachic and conceptual depth to renew them if they are "not found in the Torah itself"?