God made a promise to Abraham, because Abraham had not withheld Isaac from the Lord (Genesis 22:16). The Lord promised he would bless Abraham and multiply his descendants, and, moreover, his descendants would possess the gates of their enemies, vis-à-vis the gate of their capital cities. In other words, Abraham’s descendants would be powerful enough to conquer and rule over their enemies (Genesis 22:17). Yet, not only would the Lord bless Abraham, but he would make Abraham a blessing to all nations, in that the Savior of the world (Genesis 3:12) would come through him (Genesis 22:18). Nevertheless, we need to ask, if Esau could lose his birthright through an indiscretion brought on by a character flaw, could something similar prevent Abraham’s descendants from receiving their birthright?
Actually, this could not happen. If it could, then the Lord isn’t powerful enough to make his promises good. This would be contrary to the prime directive or principle of freedom of choice. Due to flaws in his character, man is able and often do make promises he cannot or will not keep, but God is not like mankind (Numbers 23:19). Even when we are worthy of complete destruction, God will fulfill the promises he makes to us, because his character cannot and will not change (Malachi 3:6). The Lord has purposefully refused to change what his character demands, and he will save mankind even from the total destruction, which their own choices would bring, and which we truly deserve (Hosea 13:14).
Simply put, the gifts/promises and the call of God are irrevocable (Romans 11:29). This means that God chooses a man, and will not change that choice in favor of another man, who might be easier to work with, due to a more righteous character. God chose Abraham, and, although Abraham was slow to obey, God worked with him, but he didn’t change his choice in favor of another. The same was true with both Isaac and Jacob. Once the promises came to Jacob, the promise of God was irrevocably united to the nation of Israel, which arose from his descendants.
We are told that there was a famine in the land similar to that when Abraham went down to Egypt (Genesis 26:1; cp. 12:10), so Isaac left Canaan and dwelt in Gerar, in the land of Abimelech, king of the Philistines. We aren’t told when the famine occurred, before or after the births of Esau and Isaac, so the time between the famines was at least 55 to 60 years (cp. Genesis 16:3 and 25:20), and up to a maximum of about 80 years (cp. Genesis 25:26).
Originally, Isaac may have had a mind to go to Egypt. However, the Lord appeared to him and told him, specifically, not to go there. Instead, he was to dwell in “this” land, vis-à-vis the land of the Philistines, and he would bless him there. The Lord promised to give these lands, vis-à-vis the lands of the Canaanites, to him and his descendants, and he would confirm to him the oath he had made with Abraham, his father (Genesis 26:2-3). Moreover, in reiterating those promises, the Lord told Isaac that all nations would be blessed in his Seed, vis-à-vis the Christ and Savior of the world (Genesis 26:4; cp. Genesis 3:15).
The promise was irrevocable, because of what Abraham had done in not withholding Isaac from the Lord (Genesis 26:5; cp. 22:15-18). In other words, the Lord showed Isaac that the blessings must come through him (cp. Genesis 21:12), because he is the only heir of Abraham. Abraham’s other sons, which he begat through his concubines were disinherited. Everything that the Lord promised Abraham must come through Isaac, if the Lord is able at all to perform what he says he’ll do. Finally, the text shows that Isaac took comfort in knowing this and obeyed the Lord by dwelling in the land of the Philistines, instead of going down to Egypt (Genesis 26:5-6).
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