That is what he swore by: the Fear of his father Isaac.
Now, what is interesting is the use of that word "fear," because in both cases, verses 42 and 53, the word "Fear" is actually put in place of God. In other words, the Fear of Isaac was God, but God had it written in the way (He inspired Jacob, I am sure) He inspired Jacob to use what was Isaac's outstanding characteristic. It was the fear of God. Who was the fear of God? It was Abraham's God, but expressed in Isaac's life by his fear. And so I am sure that in Abraham's family, and Isaac's family, and now in Jacob's family, what they are doing is expressing Isaac's outstanding characteristic. He feared God.
That is what Isaac feared. The fear of the Lord is the beginning of knowledge, the fear of the Lord is the beginning of wisdom, and on and on it goes. Isaac feared God. It is brought up again in Genesis 31.
Meaning the God of Isaac.
