וַיֹּ֨אמֶר יְהוָ֜ה אֶל־מֹשֶׁ֗ה קַ֚ח אֶת־כָּל־רָאשֵׁ֣י הָעָ֔ם וְהוֹקַ֥ע אוֹתָ֛ם לַיהוָ֖ה נֶ֣גֶד הַשָּׁ֑מֶשׁ וְיָשֹׁ֛ב חֲר֥וֹן אַף־יְהוָ֖ה מִיִּשְׂרָאֵֽל׃
Der Herr sprach zu Mose: Nimm alle Häupter des Volkes und lass sie hängen vor dem Herrn vor der Sonne; dass die Zornesglut des Herrn sich wende von Israel.
Rashi on Numbers
קח את כל ראשי העם TAKE ALL THE HEADS OF THE PEOPLE, to judge those who worshipped Peor (Sanhedrin 35a),
Sforno on Numbers
נגד השמש, so that the people would observe the execution of the idolaters and by not protesting their punishment achieve atonement. This would help them achieve atonement for having sinned by not protesting the sinners’ conduct beforehand.
Or HaChaim on Numbers
וישוב חרון אף השם, so that the fierce anger of G'd may turn away, etc. G'd's anger had to be turned away even after justice had been done because whereas the courts in this world can only convict people who have been warned by accredited witnesses and who have committed their sin in the presence of these witnesses, others, equally guilty, had not been dealt with. If G'd were allowed to remain angry He would give permission to the angel of death to kill all those sinners who had not been warned or whose deed had not been witnessed by their peers. If G'd's anger could be turned away, these people would remain alive at this time.