Tafsir of Al-Isra 17:19

(And whoever desires the Hereafter) — the apparent meaning, consistent with what has passed from al-Dahhak, is that it is also intended by his deeds — (the Hereafter) i.e., the abode of the Hereafter and the eternal bliss contained therein. (And strives for it with its due striving) i.e., the striving that is rightfully befitting of it, as indicated by the possessive genitive [in the Arabic text], regardless of whether the "striving" is a direct object—meaning he performs its work—or a cognate accusative (absolute object). This is realized by performing what Allah Almighty has commanded and refraining from what He, the Glorified, has forbidden. Thus, it excludes those among the disbelievers who worship through fabricated opinions, claiming they are striving for it. The benefit of the lam [preposition "for"], whether it signifies "for the sake of" or "for the specification of," is to account for intention and sincerity to Allah Almighty in the deed. Some have chosen—and it is not devoid of merit—that there is no need for what al-Dahhak considered; rather, it is better not to consider it, due to the phrase (And strives for it with its due striving). In that case, it would not be considered in what preceded either, and in this view, the verse contains a belittling of the matter of the worldly life and an exaltation of the Hereafter that is not hidden to one who reflects.

(While he is a believer) — with a correct faith unmixed with any defect. The mentioning of faith as a circumstantial clause is to signify the condition that it must accompany what was mentioned within the scope of "whoever" (man); for neither desire nor striving is of any benefit without it. In reality, it is the fountainhead from which the desire for the Hereafter and the striving for salvation therein and the attainment of reward arise. It has been narrated from some of the early scholars: "Whoever does not possess three things, his deeds will not benefit him: firm faith, sincere intention, and correct action," and he recited this verse.

(Then those) — an allusion to the "whoever" (man) by virtue of his being characterized by what preceded. The use of a term denoting distance [in the Arabic pronoun ula'ika] is to signify the loftiness of their rank and the remoteness of their status. The use of the plural is to consider the meaning, gesturing toward the reward—understood from the predicate—as occurring collectively; i.e., those who have gathered the aforementioned praiseworthy qualities—namely, the desire for the Hereafter, the beautiful striving for it, and faith— (their striving will be thanked) — that is, rewarded, accepted by Him, the Almighty, with the best of acceptance. Some have interpreted "striving" here as the action expressed by "deed," thus encompassing all that preceded; however, this is distinct from the previous "striving." Others have said: It is the same [as the previous one], and the state of being "thanked" is linked to it specifically, rather than to its two companions, to signify that it is the mainstay of the matter. "Striving" (sa'y), as al-Raghib said, is walking quickly, which is less than running; it is used for exertion in a matter, whether for good or evil, though it is most frequently used for praiseworthy acts. The poet said: "If I were to reward Alqama ibn Sa'd for his striving, I would not be rewarding him for the trials of a single day."