Musar על אבות 5:19

And our Rabbis, may their memory be blessed, stated (Avot 5:19), "Whoever possesses these three things, he is of the disciples of Abraham, our father [...] A good eye, a humble spirit and a moderate appetite." And the meaning of a humble spirit is that he does not follow his physical desire even with permissible things. [This is] like we find that Abraham stated (Genesis 12:11) "Behold I know what a beautiful woman you are" - as he had not stared at her until that day, to contemplate the character of her beauty. And our Rabbis, may their memory be blessed, stated (Yerushalmi Sanhedrin 2:3) about that which is written (II Samuel 20:3), "and they remained in seclusion until the day they died, in living widowhood" - that each day David would command that their heads be beautified and that perfumes be given to them to adorn them in order to provoke his desire and to [then] subdue it, when he would conquer his impulse for them, in order to atone for himself about the matter of Bathsheba.

ויאהב יצחק את עשו כי ציד בפיו ורבקה אוהבת את יעקב. We have an allusion here to the well-known statement in Avot 5,19 that any love which is based on something material will not endure once the object upon which it is based disappears, whereas love which is not based on something transient will endure. Isaac's love for Esau was founded on the material things Esau provided, and therefore it could not endure. This may well be the reason the Torah describes Isaac's love for Esau in the past tense, i.e. ויאהב, whereas Rebeccah's love for Jacob is described in the present tense, i.e. אוהבת, an ongoing love.