Divine involvement and prophecy

Maybe this is already spilling over into a question that needs to be given a different title, but why do you have such confidence?
I understand that there is such a chain of events here: The Torah from heaven -> What is written in the Torah is true. After all, there is divine involvement. The Torah says that there will be prophets -> So there is a prophecy, and there is no reason not to believe that these prophets were Isaiah and Jeremiah.
But the first link is weak. Why is the Torah from heaven? The only argument I know on the subject is the argument of the witness, but it proves at most that there was a Mount Sinai stand, and how can we get from here to the Torah?

This is too long a question for the answer. I extended it in the fifth conversation in the first stanza. But if you have already reached the status of Mount Sinai, the road is not long.

Sorry to interrupt. From how I understand the witness's argument, its entire validity is based on the indissoluble connection between the historicity of the Mount Sinai event and the text reported on it (which was discovered at the event). Otherwise, what do you think the witness's argument is talking about?

From my limited knowledge, the witness's argument is based on the fact that millions of people believe in revelation.