Peace Through Holy Strife
הנני נותן לו כו' בריתי שלום
"Behold, I give to him [My covenant of peace]" (Bamidbar 25:12) — "My covenant of peace."
Hashem grants Pinchas a covenant of peace, and the Sfas Emes asks how peace can be the reward.
כי א"י לבוא לברית זה בלי מחלוקת כמ"ש בזוה"ק מצה ע"ש קטטה ומריבה עם היצה"ר ואח"כ נעשה מצוה כו'
For it is impossible to arrive at this covenant without strife, as it is written in the Holy Zohar that matzah is connected to "katatah" — quarreling and contention with the yetzer hara — and only afterward does it become a mitzvah.
True peace cannot be reached without first waging war against the yetzer hara, just as the Zohar links matzah to the quarrel one wages before fulfilling the mitzvah.
והיא מחלוקת לש"ש וסופה להתקיים שע"י המחלוקת בא אח"כ למנוחה
And this is a machlokes that is for the sake of Heaven, whose end is to endure, for it is through the strife that one comes afterward to a state of rest.
A machlokes waged for the sake of Heaven is the kind that lasts, because the very struggle is what leads to lasting calm.
וזה עצמו ענין ימי המעשה ואח"כ השבת קודש יום מנוחה כמ"ש לעיל בפ' קרח מזה
This itself is the matter of the weekdays of labor, and afterward the holy Shabbos, the day of rest, as was explained above regarding this in Parshas Korach.
This is the pattern of the six weekdays of toil followed by the rest of Shabbos Kodesh.
והוא ענין אומרם ז"ל לעולם ירגיז אדם יצ"ט על יצה"ר נצחו מוטב וא"ל יקרא ק"ש
And this is the meaning of what Chazal said: "A person should always rouse his yetzer tov against his yetzer hara; if he overpowers it, good, and if not, let him recite Krias Shema" (Berachos 5a).
Chazal teach that a person must constantly stir up his yetzer tov to do battle with his yetzer hara, and if he cannot win outright he should turn to Krias Shema.
פי' אף שאינו גובר לגמרי
The explanation is that even though he does not entirely prevail,
The Gemara is acknowledging that a person may not fully defeat his yetzer hara.
מ"מ ע"י המחלוקת זוכה אח"כ בעת שבא זמן מנוחה ודביקות שאין לך אדם שאין לו שעה ואז נזכר לו זכות המחלוקת כנ"ל
nonetheless, through the strife he merits afterward, at the time when the moment of rest and dveikus arrives — for there is no person who does not have his hour — and then the merit of the strife is recalled for him, as above.
Even so, the very act of struggling earns a person the moment of rest and dveikus that eventually comes to everyone, and at that hour the merit of his earlier struggle is credited to him.
ופנחס זכה לברית שלום בלי מחלוקת ע"י הכעס והנקמה שעשה לש"ש במס"נ:
And Pinchas merited the covenant of peace without strife by means of the anger and the vengeance that he carried out for the sake of Heaven with mesirus nefesh.
Pinchas reached the covenant of peace directly, without lingering strife, because his zealous anger and vengeance were entirely for the sake of Heaven and offered with mesirus nefesh.
Summary: The Sfas Emes explains why Pinchas was rewarded specifically with a covenant of peace. True peace and rest cannot be attained without first waging strife against the yetzer hara, just as the Zohar connects matzah to the quarrel that precedes the mitzvah, and just as the weekdays of toil precede the rest of Shabbos Kodesh. This is why Chazal instruct a person to rouse his yetzer tov in battle: even if he does not fully prevail, the struggle itself earns him the eventual hour of rest and dveikus that comes to every person, when the merit of his earlier striving is recalled. Pinchas, however, attained the covenant of peace without lingering strife, because his anger and vengeance were carried out purely for the sake of Heaven and with mesirus nefesh.