According to the Gemoro in Yuma (28B) the forefathers already observed the Torah in it's entirety (according to the understanding of Ramban and the Shaloh in Toldot Adam, Beit HaBechira 4), additionally Noah must have had a certain concept of Jewish law since he was commanded about the ark in terms of the pure and impure animals.
It therefore follows logically (I think) that the average Jew was at least aware to some degree of the life/laws/wisdom of the Torah and may have even abided by it.
If so what happened by Matan Torah that we celebrate each year? It seems that it can't just be the teaching of the Mitzvot (informationally) because that wasn't new to the Jew. Is it just that it became "generally accepted practice"?
Looking for some insight
Thanks in advance