Why did Moses ask Pharaoh for a three days' journey into the desert?

Les explains that Pharaoh refused because the Jews were the backbone of Egypt's economy; they were the workers getting daily work done, while Egyptians had become an upper-class elite. Pharaoh said, "I will not let Israel go," because removing them left him with nothing. Les likens this to the American South before the Civil War and to farmers losing tractors or combines. Moses and Aaron told Pharaoh the God of the Hebrews had met with them, and asked to go three days' journey into the desert to sacrifice to the Lord their God, lest He fall on them with pestilence or sword. Les points out that three is significant in Scripture: the triune God, the Trinity, where everything begins.