What Happened to the Three Day Festival

What happened to the "three - day festival?" Contrary to what might be expected when seeing the title, this shiur is not about the "three-day yom-tov" phenomenon.  Rather, we will address the issue of the three day festival that was the premise of Yetziat Mitzrayim (the Exodus from Egypt). Moshe asked Pharaoh for permission to take the Israelites to worship God for three days in the wilderness. Do the Israelites actually do this? As we explore this topic, we also must ask what sort of literature the Torah is, and why the Song of the Sea is not found in the Book of Tehillim (Psalms).