The Mishnah belongs to the Oral Torah, but when Rabbi Yehuda Hanasi saw that the generations were degenerating, that the number of students was dwindling, that the Roman Empire was expanding, and that the people of Israel were dispersed throughout the world, he suspected that the Oral Torah might be forgotten. So, together with the Bet Din, he edited the Mishnah according to what we received at Mount Sinai so that it would not be forgotten throughout the generations.
