Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(How (will it be with them)) how shall they act, O Muhammad, (when We have brought them all together) after they die (to a Day) on a day (of which there is no doubt, when every soul) righteous or sinner (will be paid in full what it has earned) of good or evil, (and they will not be wronged) their good works will not be decreased and their sins will not be increased.
But how will it be, their predicament, when We gather them for a day, that is to say, on a day, of which there is no doubt, no uncertainty, that is, the Day of Resurrection; and every soul, from among the People of the Scripture and others, shall be paid in full, the requital of, what is has earned, [what] it has done of good or evil, and they, that is, people, shall not be wronged?, in that no good deed shall be diminished, and no evil deed shall be increased.
Chastising the People of the Book for Not Referring to the Book of Allah for Judgment
Allah criticizes the Jews and Christians who claim to follow their Books, the Tawrah and the Injil, because when they are called to refer to these Books where Allah commanded them to follow Muhammad, they turn away with aversion. This censure and criticism from Allah was all because of their defiance and rejection. Allah said next,
(This is because they say: "The Fire shall not touch us but for a number of days.'') meaning, what made them dare to challenge and defy the truth is their false claim that Allah will only punish them for seven days in the Fire, a day for every one thousand years in this life. We mentioned this subject in the Tafsir of Surat Al-Baqarah.
(And that which they used to invent regarding their religion has deceived them.) meaning, what caused them to remain on their false creed is that they deceived themselves, believing that the Fire will only touch them for a few days for their errors. However, it is they who have invented this notion, and Allah did not grant them authority to support this claim. Allah said, while threatening and warning them,
(How (will it be) when We gather them together on the Day about which there is no doubt (i. e. the Day of Resurrection).) meaning, what will their condition be like after they have uttered this lie about Allah, rejected His Messengers and killed His Prophets and their scholars who enjoined righteousness and forbade evil Allah will ask them about all this and punish them for what they have done. This is why Allah said,
(And each person will be paid in full what he has earned And they will not be dealt with unjustly.).
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
That is, "They are asked to acknowledge the Book of Allah as the final authority and bow before its decrees and accept as true whatever is proved to he true by it, and reject whatever is proved to be false by it. "It should be noted that here by the Book of God is meant the Torah or the Gospel and by "the people who have received a share of the knowledge of the Book" are meant the learned people of the Jews and the Christians.
As such people regard themselves to be the favourites of God, they delude themselves that they are going to enter into Paradise anyhow, irrespective of the quality of their deeds. They foolishly believe that the fire of Hell dare not touch them because they are "true" believers and the children of such pious ancestors, and the followers of such and such prophets and the disciples of such and such saints, etc., etc. And if at all they are cast into Hell, they argue, they will be kept there only for a few days and that, too, to be cleansed of the impurity of sins and then will go into Paradise permanently. Such misleading ideas and conceptions have made them so bold that they commit the gravest crimes and the most heinous sins fearlessly: so much so that they openly disown the Truth without the least fear of Allah.
But how will it be when We gather them for a day of which there is no doubt and every soul shall be paid in full what it has earned and they shall not be wrongedḍ This address is remarkable because by it He gives information about the imposing grandeur and intensity of the [Day of Gathering] at which point the intellects [of those who turned away] will be perplexed their innermost selves astonished their pretensions cut off their hearts torn from their hidden places and [their souls] will rise to their collar bones. Then there will be what will meet them from the reckoning and censure al-ḥisāb wa-lʿitāb the torment and punishment al-ʿadhāb wa-l-ʿiqāb and the lack of honoring and approval ʿadam al-ikrām wa-l-ījāb etc. The resurrection of the disbelievers will take place on the Day of Gathering while the resurrection of the lovers takes place in the present moment; to explain this fully would take a long time.