The story of Pinchas is one of zealotry and rashness—two traits that are often viewed negatively in modern sentiments.
Rashi (Bamidbar 25:11) quotes the Talmud’s (Sanhedrin 82b) concerning the accusation expressed by the various tribes, saying: “Have you seen the son of Puti, whose mother’s father [Jethro] fattened (פִּטֵּם) calves for idols, and who killed a chieftain of an Israelite tribe? For this reason, Scripture traces his pedigree to Aaron”
What is expressed in this is that when views the trait of zealotry there are two actions that may seem similar, but are in actuality conceptually entirely dissimilar. Both the villain and the hero carry a sword at their side and are times violent, however, one valiantly fights for an honorable cause, while the villains drive is the evilness embedded in his soul.
Pinchas’ actions of killing Zimri can be seen as wanton murder and disregard for his own life, placing himself in danger or as a complete dedication to the almighty that surpasses any logical considerations.
The difference between the two actions is not in the external act itself but the drive of the actions. The tribes intimated that Pinchas’ capacity to nonchalantly kill sinners came from the trait of his maternal grandfather who fattened animals for the slaughter.
It was this intense cruelty, they said, that was the root of Pinchas’ actions, not his love for G-d. It is for this reason that the Torah states that he was the son of Aaron, to testify that Pinchas was driven by love of G-d and His people not hate.
For this reason, he was rewarded in becoming a Kohen. Just as the father of all priests loved peace and pursued it, so too each Kohen is referred to as a man of kindness.
The lesson is clear; we should not be quick to judge the actions of individuals that are suspect in our eyes. While we may assume the worst in our fellow, the drives behind the our fellows actions may be very different than our initial conception.