بِنَصۡرِ ٱللَّهِۚ يَنصُرُ مَن يَشَآءُۖ وَهُوَ ٱلۡعَزِيزُ ٱلرَّحِيمُ ٥
In the victory of Allāh.1 He gives victory to whom He wills, and He is the Exalted in Might, the Merciful.
Translation: Saheeh International (English)
1 i.e., the victory given by Allāh to a people of the Scripture (Christians) over the Magians of Persia.
Each word's meaning and sound
They will be happy because of the help of Allah being with the Romans due to them being the people of the book. Allah helps whoever He wishes against whoever He wishes; He is the Almighty who cannot be overcome, the Merciful towards His believing servants.
Al-Mukhtasar in interpreting the Noble Quran