Why Abraham Withheld His Blessing from Isaac

Another interpretation of (Genesis 12:2): "And be a blessing." The Holy One, blessed be He, said to him: From the hour that I created My world until now, I have been required to bless My creatures, as it is said, "And God blessed them" (Genesis 1:28); and I blessed Noah and his sons, as it is said, "And God blessed Noah" (Genesis 9:1). From here onward, you are appointed over the blessing, as it is said, "And be a blessing." But he did not do so. Rather, when Isaac arose, Abraham sought to bless him; when he foresaw that Esau and Jacob would arise from him, he did not bless him. A parable: to what is the matter like? To a king of flesh and blood who had an orchard, and he gave it to a tenant farmer to guard it. And within the orchard there was a tree of the drug of death and a tree of the drug of life, clinging one to the other. The tenant said: What shall I do? To water this one and leave that one I cannot. Rather, I will leave them until the owner of the orchard comes, and what he knows, he will do. So Abraham said: If I bless Isaac, Jacob and Esau will arise from him. Rather, I will leave him until the Holy One, blessed be He, desires it, and He will bless him. When Abraham and Isaac had departed, the Holy One, blessed be He, blessed Jacob Himself, as it is said, "And God appeared to Jacob... [and blessed him]" (Genesis 35:9).