In Genesis 15:13, the LORD revealed to Abraham that his descendants will live and serve in a foreign land for 400 years. This prophecy was given even before Isaac was conceived. God had made an everlasting covenant with Abraham in Genesis 17:7 that He will be a God to Abraham and to his offsprings thereafter. Why then did God allow his people to become slaves for 400 years? The children of Israel landed up in Egypt not because of their sins. It started off so right, with Joseph being the Prime Minister and provided for all his brothers and their families. Yet, who would imagine that such a blessed beginning could end up having their descendants becoming slaves? 

The bible did not give any reason why things had to happen that way where the children of Israel had to suffer for 400 years. All we know is that in Genesis 15:14, the LORD promised that the children of Israel will come out of the land with great wealth. 

The most powerful civilisation in that era was Egypt. That was the country were you will learn all kinds of knowledge –military, trade, scrupting, mining, art & craft, technology, irrigation, construction, medicine, education and many others. It was God’s will that His people should gain all these knowledge so that they could acquire all the skills and knowledge needed to enter their promised land. However, this is a fallen world. Ancient Egyptian religion was a complex system with Egyptians interacting with many deities. For a people of God in such a land, it is inevitable that the forces of darkness will persecute the people of God.

God’s plan was for the children of Israel to be equipped. God’s plan was never for them to be slaves. In a fallen world, persecutions are in evitable. Nonetheless, God’s protection was always upon the children of Israel and God always has a deliverance plan. When God’s objective was fulfilled, the deliverance plan would kick in. God raised Moses to deliver the children of Israel out of Egypt.