Tafsir of Al-Baqarah 2:218

(Indeed, those who have believed) Ibn Abi Hatim and al-Tabarani recorded in al-Kabir, through a hadith of Jundub ibn Abdullah, that this was revealed regarding the sariyyah (expedition) when it was thought that even if they were saved from sin, they would have no reward.

(And those who have emigrated) meaning: they parted from their homelands. Its origin is al-hajr (abandonment), the opposite of al-wasl (connection).

(And struggled in the way of Allah) for the exaltation of His religion. The relative pronoun is repeated despite the fact that the referent is the same, in order to magnify the status of emigration and struggle; it is as if—even though they are conditional upon faith in reality—they are independent in realizing hope. Emigration was placed before struggle because it precedes it in occurrence, just as faith precedes them both.

(Those) who are described with these glorious attributes (hope for the mercy of Allah) meaning: they anticipate the attachment of His mercy, glorified be He, to them, or His reward for their deeds, among which is that expedition during the sacred month. Some have restricted it to that [expedition] based on what al-Zuhri narrated: that when Allah the Exalted relieved the people of that expedition from the grief they were in, they aspired to His reward, so they said, "O Prophet of Allah, do we aspire that this be a struggle for which we are given the reward of the emigrants in the way of Allah the Exalted?" Then Allah the Exalted revealed this verse. It is not hidden that the general application is more beneficial.

He affirmed hope for them rather than the attainment of what is hoped for, as an indication that the deed does not necessitate it, for there is no inherent entitlement through it. Furthermore, it does not definitively prove the realization of the reward, as there is no rational correlation between them; it is merely His grace, glorified be He. Especially since the consideration is for the endings, and perhaps there may occur after that which necessitates the nullification [of deeds]. This has indeed occurred—and we seek refuge in Allah the Exalted—frequently, so one should not rely [solely] upon the deed.

(And Allah is Forgiving, Merciful) This is a conclusion to what preceded and an emphasis upon it. Forgiveness was not mentioned in what preceded because the hope for mercy implies it. The attribute of forgiveness was placed first because the warding off of evils takes precedence over the bringing about of benefits.