3:153
Behold! ye were climbing up the high ground, without even casting a side glance at any one, and the Messenger in your rear was calling you back. There did Allah give you one distress after another by way of requital, to teach you not to grieve for (the booty) that had escaped you and for (the ill) that had befallen you. For Allah is well aware of all that ye do.
To understand the proper sequence of this verse, it is necessary to reconsider the preceding verse (3:152), which states, “then Allah diverted you from them in order to test you” (thumma ṣarafakum ʿanhum li-yabtaliyakum). This statement indicates that the believers’ experience of defeat occurred as a consequence of their disobedience and momentary lapses. Rather than immediately punishing them for these shortcomings, Allah allowed them to undergo a trial intended as a test through which they might ultimately receive forgiveness and benefit from His grace and favor.
The subsequent phrases—“when you were fleeing” (idh tuṣʿidūna) through “there did Allah give you one distress after another” (fa-athābakum ghammam bi-ghammin)—describe the nature and details of this trial. These expressions portray the believers’ retreat and the series of hardships that followed during the battle. Finally, the statement “so that you would not grieve over what had escaped you or what had befallen you” (li-kaylā taḥzanū ʿalā mā fātakum wa lā mā aṣābakum) highlights the moral lesson embedded in this experience. The trial served to instruct believers to remain steadfast and not lose heart over losses or misfortunes, provided they continue to follow the teachings of Islam sincerely and persevere in its cause.
References:
Islahi, Amin Ahsan. Pondering Over The Qur’an: Surah Ali Imran (pp. 270-271). Islamic BookTrust. Kindle Edition.