וְהָ֣יוּ לִ֗י אָמַר֙ יְהוָ֣ה צְבָא֔וֹת לַיּ֕וֹם אֲשֶׁ֥ר אֲנִ֖י עֹשֶׂ֣ה סְגֻלָּ֑ה וְחָמַלְתִּ֣י עֲלֵיהֶ֔ם כַּֽאֲשֶׁר֙ יַחְמֹ֣ל אִ֔ישׁ עַל־בְּנ֖וֹ הָעֹבֵ֥ד אֹתֽוֹ׃
Y serán para mí especial tesoro, ha dicho SEÑOR de los ejércitos, en el día que yo tengo de hacer: y perdonarélos como el hombre que perdona á su hijo que le sirve.
Rashi
for that day when I make a treasure that I have stored and put away, with which to pay My reward. There I will show you what the difference is between a righteous man and a wicked man.
Tze'enah Ure'enah
“They shall be Mine, says the Lord of Hosts on the day, etc.” [3:17]. It will be in that day, on the day that I will judge the evildoers, the righteous will be a people praised by Me and I will have mercy on them, like a father has compassion on his son that has been faithful to his father.