D’var Torah Ki Tetze

You shall send away the mother, and [then] you may take the young for yourself, in order that it should be good for you, and you should lengthen your days. (Deuteronomy 22:7 )
The Gaon of Vilna notes that the Torah presents the promise of length of days as the reward for fulfillment of two miztvot only: sending away the mother bird and honoring one's father and mother. [Exodus 20:12; Deuteronomy 5:16]
The reason for this, explains the Gaon, is that "completion is recognizable within a person only when he possesses two contradictory traits, mercy and cruelty." A person who acts exclusively with the trait of mercy cannot be considered righteous, since he can be seen as acting solely in accordance with his inherent nature. However, one possesses contradictory traits, such as mercy and cruelty, and he chooses to act in accordance with God's mitzvot, demonstrates that he is truly righteous.

The mitzva of honoring one's father and mother is rooted in mercy, that children will have mercy on his parents, who brought him into this world. In contrast, the mitzva of sending away the mother bird is a "cruel mitzva," since "there is great cruelty in taking the fledglings and sending away the mother," since the Torah could have absolutely forbidden taking the fledglings.
Therefore, these two mitzvot express the contradictory traits of mercy and cruelty, and the person who "possesses these two qualities has achieved completion." For this reason, the Torah presents length of days specifically as the reward for these two mitzvot.
The Gaon adds that this approach explains the words of the angel to Abraham following the binding of Isaac: "… for now I know that you are a God-fearing man, and you did not withhold your son, your only one, from Me." [Genesis 22:12] At first glance, the angel's declaration is surprising, since Abraham " already was righteous (and God-fearing)." Rather, prior to binding Isaac, Abraham "was only merciful, and the trait of cruelty was not evident within him," so that Abraham could not have been considered to be completely righteous. After acting with cruelty in binding his beloved son on the altar, Abraham demonstrated that he possessed the trait of cruelty as well and thereby revealed himself as a truly righteous person. (David Magence)

Shabbat Shalom!
The Va’ad