"{And it is not for the believers to go forth in their entirety}" until the end of the verse. Some interpret it as follows:
When the Messenger of Allah (peace be upon him) returned from Tabuk, and Allah (Glorified and Exalted be He) had revealed regarding the hypocrites who stayed behind what He revealed, the believers said: "No, by Allah, Allah (Glorified and Exalted be He) shall never see us lagging behind from an expedition the Messenger of Allah (peace be upon him) goes on, nor from any military detachment." Thus, the Messenger of Allah (peace be upon him) commanded the military detachments to depart, so the Muslims set forth to the last man, leaving the Prophet of Allah (peace be upon him) alone. Then Allah (Glorified and Exalted be He) revealed: "{And it is not for the believers to go forth in their entirety}" meaning: all of you, and leave you alone in Medina. "{So why}" meaning: why is it not that "{there has not gone forth from every group among them a party to study religion}" so that those who stay behind may attain understanding, "{and to warn their people when they return to them}" from their military expedition? Meaning: the one who remains behind teaches the one who went on the expedition what was revealed of the Quran after his departure.
Surah al-Tawbah from verse (123) to verse (125).
﴿وَمَا كَانَ الْمُؤْمِنُونَ لِيَنْفِرُوا كَافَّةً﴾ الآيَةَ، تَفْسِيرُ بَعْضِهِمْ:
أَنَّ رَسُولَ اللَّهِ ﷺ حِينَ رَجَعَ مِنْ تَبُوكَ وَقَدْ أَنْزَلَ اللَّهُ ﷿ فِي الْمُنَافِقِينَ الَّذِينَ تَخَلَّفُوا عَنْهُ مَا أَنْزَلَ - قَالَ الْمُؤْمِنُونَ: لَا وَاللَّهِ لَا يَرَانَا اللَّهُ ﷿ مُتَخَلِّفِينَ عَنِ الْغَزْوَةِ يَغْزُوهَا رَسُولُ اللَّهِ ﷺ أَبْدًا وَلا عَنْ سَرِيَّةٍ. فَأَمَرَ رَسُولَ اللَّهِ ﷺ السَّرَايَا أَنْ تَخْرُجَ فَنَفَرَ الْمُسْلِمُونَ مِنْ آخِرِهِمْ، وَتُرِكَ نَبِيُّ اللَّهِ ﷺ وَحْدَهُ، فَأَنْزَلَ اللَّهُ ﷿: ﴿وَمَا كَانَ الْمُؤْمِنُونَ لِيَنْفِرُوا كَافَّةً﴾ أَيْ: جَمِيعًا، وَيَذَرُوكَ وَحْدَكَ بِالْمَدِينَةِ ﴿فلولا﴾ فَهَلا ﴿نَفَرَ مِنْ كُلِّ فِرْقَةٍ مِنْهُمْ طَائِفَةٌ لِيَتَفَقَّهُوا فِي الدِّينِ﴾ ليتفقه المقيمون ﴿وينذروا قَومهمْ إِذا رجعُوا إِلَيْهِم﴾ مِنْ غَزَاتِهِمْ. أَيْ: يُعَلِّمُ الْمُقِيمُ الْغَازِي مَا نَزَلَ بَعْدَهُ مِنَ الْقُرْآن.
سُورَة التَّوْبَة من الْآيَة (١٢٣) إِلَى الْآيَة (١٢٥).
