What is the meaning of the noble verse: "Say, 'Shall We inform you of the greatest losers in [their] deeds? [They are] those whose effort is lost in worldly life, while they think that they are doing good work,'" and who is meant by it and who are they?

Al-Qurtubi, in his interpretation of the verse: "Say, 'Shall We inform you of the greatest losers in [their] deeds?'" (Quran 18:103), holds that the verse indicates that some people perform deeds they believe to be righteous, yet these deeds are rendered invalid due to corrupt belief or hypocrisy, the intent here being disbelief (kufr). The Salaf differed regarding the identification of "the greatest losers in [their] deeds." Some were of the view that they are the Jews and Christians, or the disbelievers of Mecca, while others believed them to be the Khawarij or monks. However, the verse: "Those are the ones who disbelieved in the verses of their Lord and [in] His meeting, so their deeds became worthless" (Quran 18:105), suggests that the intended meaning is the polytheists of Mecca who worshipped idols, as they are the ones who disbelieved in Allah's verses and His meeting.