Why did Jacob and his family move down to Egypt during the famine?

Les explains that Joseph was down in Egypt with all kinds of food and grain stored up during the famine that covered that whole part of the world. The sons had been down to get grain, found out Joseph was there, and Joseph invited Jacob and the rest of the family to come down into Egypt and take part of all the food and everything supplied. But Les also points out God’s purpose: God spoke to Israel, that is Jacob, in visions of the night and said, “Jacob, Jacob,” and “I am God of thy father. Fear not to go down into Egypt.” This was a change from earlier instruction not to go to Egypt and to stay in the land of promise, because now it was time for the nation of Israel to explode in population. God had told Abraham it would be down in Egypt, and He promised Jacob, “I will there in Egypt make of thee a great nation.” Les says this shows where the nation of Israel began to come into bloom—in Egypt. Up to that time there were only Abraham, Isaac, and Jacob; Jacob came back with the 12 sons and their children, still not much of a nation.