Few professions are as
cruel and inhumane as the fattening of calves for slaughter. So when
Pinchas slew Zimri, many said: "Look at this holy zealot! He acts as if
motivated by the desire to avenge the honor of G-d and save the people,
but, in truth, he has merely found a holy outlet for his cruel and
violent nature. After all, it's in his blood--just look at his maternal
grandfather..." So G-d described him as "Pinchas the son of Elazar the
son of Aaron" in order to attest that in character and temperament he
actually took after his paternal grandfather--the compassionate and
peace-loving Aaron.
The true greatness of Pinchas lay in that he acted in complete
opposition to his nature, transcending his inborn instincts to bring
peace between G-d and Israel.
(The Lubavitcher Rebbe)