-After Avrahom passed the test of attempting to sacrifice Yitzchock, he was told “Now I know that you fear G-D.”
-Avrahom’s whole essence and all his actions always stemmed from the attribute of Chesed-Kindness. It was only after he was able to preform a cruel act for the sake of Heaven, that he was told “Now I know.” For until now it was not known if he could do a complete act of DIN.
-This is also the reason why the two commandments that offer long life as the reward are Honoring Parents and Shiluach Haken (sending away the mother bird and taking the eggs, a rather cruel act).
-Meaning , the way to attain a long life is only by achieving completion, for otherwise one is eventually overcome by the elements he did not completely master. Therefore one has to show that he can serve G-D through both Chesed and Gevurah.
-The third commandments of honest measurements is the ability to balance both sides and walk in the middle.

(Kol Eliyaho - Vayerah GRA of Vilnah)