Issac was the son of Abraham and God promised Issac just as He promised Abraham his descendants will be as numerous as the stars in the sky and all the nations will be blessed through him. And God's promise was fulfilled when Jesus came down and died for our sins. Since Issac and Abraham was the ancestor of Jesus, so their descedants include all those who would trust in Jesus. It was a wonderful blessing that God gave to them!
Abraham had the promise of God and Issac inherited the promise because he was the son of Abraham and Sarah and he had his birthright. Just like this:
Abraham=>Issac
After Abraham died, Issac was married to Rebekah, and they had two sons, the elder one called Esau and the younger one called Jacob. According to the customs and traditions(not from the mouth of God), Esau being the eldest has the birthright, and he is suppose to "inherit" the promise of God when Issac dies. So the chart will be like this:
Abraham=>Issac=>Esau
However, Esay did not inherit the promise. Why? Lets focus on Esau and Jacob's life from here on..
Esau was the eldest son of Issac, He is a cunning hunter and a man of the field. In the original Hebrew text, Esau is known as a wild and undisciplined man,and Jacob is a plain man who dwells in tents, known as a quiet and mature individual who is sensible, diligent, dutiful and peaceful. But Issac favored Esau.
So one day, when Jacob cooked some stew, Esau came back from the field and he was starving and faint. So Esau asked Jacob to feed him. And Jacob asked Esau to sell him his birthright if he wants food. Because of that, Esau sold his birthright to Jacob and he later on became the one who rightfully inherited that wonderful promise, thus changing the arrow chart like this:
Abraham=>Issac=>Jacob
Esau forsaken that wonderful promise because of FOOD! Esau gave up his birthright! And later on he'll be the father of the Edomites instead of the Israelites(the people of God). How sad is that?!
That's history but it still is the same. The natural heart who doesn't have God, like Esau, couldn't not see the value on the things of God, the promises and things of God are vague, powerless, valueless. But the heart that longs for God, like Issac, will be able to see the valueble worth of following God and cherishing His things and will fight for it.
Therefore, hold on to God even when it is tough! Don't be like Esau who has forsaken that wonderful promise because of his immediate "needs". But rather look towards God and depend and trust and hold on to His promises, just like Issac.
HOLD ON EVEN WHEN IT IS TOUGH!