This is the legacy he left to his descendants so that they may turn (to God).
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Tafseer
'Abdullāh Ibn 'Abbās / Muḥammad al-Fīrūzabādī
تفسير : (and he made it) i.e. “there is no deity except allah” (a word enduring) firm (among his seed) the offspring of abraham, (that haply they might return) that his folk may return from their disbelief to the belief in allah's divine oneness.
Jalāl al-Dīn al-Maḥallī
تفسير : and he made it, namely, the statement of the affirmation of [god’s] oneness, understood from his words, i shall indeed depart to my lord; he will guide me [q. 37:99], a word enduring among his posterity, his descendants, and thus there still remains among them those who affirm the oneness of [god]; that perhaps they, that is, the people of mecca, might recant, what they follow [and return] to the religion of their forefather abraham.