The Three Days of Preparation and the Festival of the Giving of our Torah indeed come once a year, but there is a small-scale version of this preparation and of Mattan Torah every day.
The holy Torah is not a collection of laws for special occasions. It embraces the totality of the Jew, from his first moment to his last, and in all the minute aspects of his day-to-day life.
The Israelites understood that there could be no real freedom -- freedom from any fear of oppression by others, and freedom from one's own evil inclinations -- except through laws of justice and righteousness.