"Unless you are surrounded," meaning: unless you are overcome regarding him.
"So when they had given him their pledge," meaning: their covenant, "Allah is Witness over what we say," meaning: a Guardian over this covenant.
﴿إِلَّا أَن يحاط بكم﴾ أَيْ: تُغْلَبُوا عَلَيْهِ.
﴿فَلَمَّا آتَوْهُ موثقهم﴾ عَهْدَهُمْ ﴿قَالَ اللَّهُ عَلَى مَا نقُول وَكيل﴾ أَي: حفيظٌ لهَذَا الْعَهْد.
