Why couldn't God use Esau even if Esau was a morally better man than Jacob?
God could not use Esau because Esau had no faith, and without faith it is impossible to please God. Even if Esau had been morally better than Jacob, his lack of faith disqualified him; God requires faith and cannot use anyone who is destitute of it.
Les explains that no matter how morally good Esau may have been, and he doubts Esau was because of his marrying the Canaanites, even if Esau was a better man than Jacob, God could not use him because he had no faith. Hebrews 11:6 says that without faith it is impossible to please God. Les applies this same principle today: people are turned off by Christianity and spiritual things because they are destitute of faith and can no longer believe this is the Word of God. They have become so intellectual and scientifically minded that they demand proof. But God does not have to prove anything; God is sovereign, He has spoken it, and He has every right to expect mankind to believe it. Consequently, if we have not got faith, there is no way we can please Him, nor could Esau. Les also notes that Jacob, when he said he was Isaac's firstborn son according to how God mandated it, did not lie.
But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.