Where do we get the Mitzvah to hear the Shofar, the Torah says that it is a day of blowing Shofarot… but that is a commandment to blow , not to hear?
You can't learn practical Mitzvot from the written Torah without the oral Torah's interpretation. When the Torah writes [Bamidbar 29] Yom Terua Yihiye Lachem – a day of a Shofar blast it shall be for you, Moshe Rabenu on Har Sinai was taught the meaning is every Jew needs to listen to the Shofar blast; Moshe then delivers this information on to all Jews. That is the way almost all of the Mitzvot are interpreted from the written Torah to practice. [Try to explain the word of the Torah – lay Tefilin – without the oral interpretation…]