1)
How will they be justified and boast via Hashem?
1.
Rashi: In the promise of the support of His love, they will find Tzedakah and boast in His strength.
2.
Radak: The nations will be ashamed, but Zera Yisrael will be justified via serving Him and boast in Him in front of the nations, for they clung to Him even in their Galus - "Im Shachachnu Shem Elokeinu va'Nifrosh Kapeinu l'El Zar" (Tehilim 44:21).
3.
Malbim: Aside from being justified via the good deeds, they will boast that they never denied Him.
