One translation puts that beginning of verse 19 saying, "I have singled him out [that is, God has singled Abraham out], that he may instruct his children and his posterity to keep the way of the Lord by doing what is just and right." Now, Isaac learned his lessons well. Isaac did what Abraham said.
The first thing I want you to get from this is that God gave Isaac an instruction that He wanted Isaac to do. Now, what God instructed Isaac to do went against the grain of nature and at the same time, it went against the grain of what it was natural for Isaac to want to do. The setting is a famine. The other time there was a famine is when Abraham went to Egypt. That is what it is referring to when it says there in verse 1 that "there was a famine in the land, besides the first famine." See, this is another famine, a whole generation later, and when that first famine took place, that is what motivated Abraham to go down into Egypt.
Now because a famine was going on, and I am sure without it having to be written, that it was noised around the area, it was news, that if you go down to Egypt it is nice and green down there, they are getting rain, and you can farm or shepherd right around the River Nile and everything is going to be okay. So the weather, that is, the famine, and Isaac's desire for self-preservation, not only for himself, but for all of those people who are counting on him to support them, was to go down to Egypt. God said, "No, you're going to stay right here right in the midst of the famine."
So, what was God doing? He was putting Isaac to a pretty severe test, to say the least, because he had already journeyed from his own home area to the land of the Philistines in Gerar. The land of the Philistines was over near the Mediterranean Sea. His own area was around Beersheba and Bethel in the middle of the country. And so he had journeyed over to the westward, to the Mediterranean Sea to the area of Gerar and the Philistines. And by this time, Egypt was only a hop, skip, and a jump away a little bit to the south. He was almost there before God said "no."
Now if he was already on the way, then the famine had been in the land long enough that it is very likely that their supplies were running pretty low, not only the supplies to feed the sheep, but probably also the supplies to feed the people as well.
What did Isaac do? Well, he did what God said. He went against what everybody else was doing and what his own nature was telling him to do. He stayed in Gerar, he submitted. Now it is right here that we come face to face with Isaac's strength. Isaac's outstanding characteristic is his trustful and faithful submission to God.
This was long before the Ten Commandments were given. People may scoff at that today. They may not think that this is true, but it is true! We also see from this account that God is fully able to keep all the promises that He makes. God definitely gave Abraham His laws and commandments, and Isaac and Jacob kept them, too!
