Why did they ask Pharaoh to leave for three days

Hello, During the Exodus from Egypt, Moses was instructed to ask Pharaoh for permission to leave for the desert for 3 days to offer sacrifices. I would like to know if there are any explanations from the commentators as to why they asked to leave for sacrifices and not, for example, to leave Egypt entirely?

Hello 

There are several explanations for this, and we will present some of them:

The Midrashim explain that the reason was so that later Pharaoh would chase after them and receive his punishment at the Red Sea, which would not have happened if he had allowed them to leave permanently. 

Abarbanel explains that this was to demonstrate to everyone why Pharaoh and Egypt deserved such punishments, as they did not agree even to a three-day departure. 

Alshich explains that it was so that the Egyptians would agree to lend the Israelites silver and gold vessels, as if they knew they were leaving permanently, they would not have lent them. 

In the book "Emek Davar," the language of the verse is specified: 'And you and the elders of Israel shall come to the king of Egypt, and you shall say to him: The Lord, the God of the Hebrews, has met with us, and now let us go, we pray you, three days' journey into the wilderness, that we may sacrifice to the Lord our God.'

Thus, they did not say in the name of the Lord that they would leave only for three days, but the Lord commanded us to come to serve Him, and we ask that it be for three days. And if the Lord wills, we will serve Him for a longer time. 

Exodus 3:18, commentators there.