What did God tell Isaac about going into Egypt?

God told Isaac, 'Don't go into Egypt.' The instruction was a prohibition against going down to Egypt. When they tried it, they got into trouble and had to hightail it back to Canaan. This contrasted with God later telling Jacob not to fear going into Egypt, where He would make of him a great nation.

Les explains that God had been telling Abraham, and then He told Isaac, 'Don't go into Egypt.' When they tried it, they got into trouble until they hightailed it back to Canaan. Later, God tells Jacob, 'Don't be afraid to go down into Egypt, for there in Egypt I will make of thee a great nation.' That is exactly what happened: after some 215 years, the children of Israel in Egypt grew so numerous that Moses led out a company of anywhere from 5-7 million people, the biggest nation in the then-known world. The Abrahamic covenant was repeated to Isaac and then to Jacob.

Why did God tell Jacob not to be afraid to go down to Egypt?

God told Jacob not to fear going down to Egypt because He promised to make Jacob a great nation there, fulfilling the Abrahamic covenant. This assured Jacob that Egypt would be a place of growth and blessing, not harm, and after 215 years Israel came out as a vast company of millions.