Why did God tell Moses to lead the Israelites out of Egypt?

Answer 1

It is related to Moses having reached a level of prophecy higher than that of any other prophet (Numbers ch.12, Deuteronomy ch.34). Because of that, he was chosen by God as the person most suitable to carry out the greatest missions (the leading of the Israelites out of Egypt and then across the Sea of Reeds, the receiving of the Torah, and the leading of the Israelites throughout the next forty years). See also:

Biography of Moses

Answer 2

Exodus 3:7-10 argues that God did this because He was reacting to the suffering of the Israelite people in Egypt and to direct their passage to the Promised Land. See the excerpt below from the NIV translation:

7 The Lord said, “I have indeed seen the misery of my people in Egypt. I have heard them crying out because of their slave drivers, and I am concerned about their suffering. 8 So I have come down to rescue them from the hand of the Egyptians and to bring them up out of that land into a good and spacious land, a land flowing with milk and honey—the home of the Canaanites, Hittites, Amorites, Perizzites, Hivites and Jebusites. 9 And now the cry of the Israelites has reached me, and I have seen the way the Egyptians are oppressing them. 10 So now, go. I am sending you to Pharaoh to bring my people the Israelites out of Egypt.”

Answer 3

It was his will.