Tafsir of Al Imran 3:143

(And you had certainly wished for death): This is an address to a group of believers who did not witness the Battle of Badr, as they did not expect war when the Messenger of Allah (may Allah exalt him and grant him peace) set out for it. When the event occurred, they regretted it and used to say: "Would that we had been killed as the companions of Badr were killed, and that we had been martyred as they were martyred." So, when Allah the Exalted caused them to witness [the Battle of] Uhud, none of them remained [steadfast] except those whom Allah the Exalted willed among them.

The intended meaning of "death" here is death in the path of Allah the Exalted, which is martyrdom. There is no harm in wishing for it, and the objection that wishing for it implies the victory of the disbelievers is invalid. For the intention of the one wishing is solely to attain the honor of the martyrs; nothing else crosses his mind or concern. Just as one who drinks a medicine made by a Christian, for example, intends [to attain] healing, not to benefit him or promote his craft. This wish occurred from Abdullah ibn Rawahah, one of the prominent companions, and he was not rebuked for it. It is also permissible that "death" refers to war, for it is one of its causes; the words of al-Rabi’ and Qatadah suggest this, in which case the one wishing for it is wishing for war, not death itself.

(Before you encountered it): This is linked to "you wished for," explaining the reason for their boldness in wishing; meaning, before you witnessed it and knew what it was. It has been recited with a damma on the lam (ta-laquhu) based on the omission of the genitive-linked noun (mudaf ilayh) and the intention of its meaning. And "that you encounter it" at that time is a badal ishtimal (permutation of inclusion) for "death"; meaning, you wished for death—that you encounter it—before that. It was also recited as talaqawhu, from the reciprocal form (mufa'ala) that occurs between two parties, and "whoever met you, you have met him." It is also permissible for it to be like the structure of "I traveled" (safartu). The pronoun refers to death. It has been said: [it refers] to the enemy, which is understood from the speech, but this is of no consequence.

(Then you have seen it): Meaning, what you wished for of death, by witnessing its causes or [by witnessing] the causes of its causes. The fa (then) is fasiha (eloquent/explanatory), as if it were said: If you were truthful in that wish of yours, then you have [now] seen it. The preference for "seeing" (ru'ya) over "encountering" (mulaqat) is either to point to their defeat or to emphasize their witnessing of it, such as the qualification of this by His saying, the Exalted: (And you are looking on), as it is in the position of a state (hal) from the pronoun of the addressed. That is: you saw it while observing it directly. This is similar to your saying: "I saw it while there was no defect in my eye," meaning I saw it a true vision, with no concealment or ambiguity in it. It has been said: (looking on) means contemplating and reflecting, meaning: while you were contemplating the situation as it was. It has also been said: its meaning is (while you were looking) at Muhammad (may Allah exalt him and grant him peace).

In any case, the intent of this speech is to rebuke those who fled for wishing for martyrdom while they did not stand firm to be martyred, or for wishing for war and causing it, then showing cowardice and fleeing—not for wishing for martyrdom itself, as that is something for which there is no rebuke, despite what some have imagined.