Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(And We set a just balance for the Day of Resurrection) on the Day of Judgement, there will be a balance which will weigh only good and bad works (so that no soul is wronged in aught) no one will have his good works diminished nor his evil works increased. (Though it be of the weight of a grain of mustard seed, We bring it) We requite for it. (And We suffice for reckoners) We are enough as Preserver and Knower.
And We shall set up the just balances, the equitable ones, for the Day of Resurrection, that is, on it, and no soul shall be wronged in any way, neither by deducting a good deed [from its record], nor by adding [to it] an evil one; and even if it, the action, be the weight of a [single] mustard seed, We shall produce it, with its full weight, and We suffice as reckoners, to count all things.
How the Idolators are deceived by their long and luxurious Lives in this World, and the Explanation of the Truth
Allah explains that they have been deceived and misled by the luxuries that they enjoy in this world and the long life that they have been given, so they believe that they are following something good. Then Allah warns them:
(And indeed We have destroyed towns round about you, and We have shown the Ayat in various ways that they might return.) 46:27 Al-Hasan Al-Basri said: "This means the victory of Islam over disbelief.'' The meaning is: Do they not learn a lesson from the fact that Allah supported those (believers) against their enemies, He destroyed the disbelieving nations and the evil-doing townships, and He saved His believing servants So Allah says:
(Is it then they who will overcome) meaning, on the contrary, they are the ones who will be overcomed, who will be defeated, humiliated and brought low.
قُلْ إِنَّمَآ أُنذِرُكُم بِالْوَحْىِ
(Say: "I warn you only by the revelation.'') meaning, `I only convey to you the warning of Allah's punishment and vengeance, and this is no more than that which Allah reveals to me.' But this is of no benefit to the one whom Allah has made blind and has put a seal over his hearing and his heart. He says:
(And if a breath of the torment of your Lord touches them, they will surely, cry: "Woe unto us! Indeed we have been wrongdoers!'') If these disbelievers were affected by the slightest touch of Allah's punishment, they would confess their sins and admit that they had wronged themselves in this world.
(And We shall set up Balances of justice on the Day of Resurrection, then none will be dealt with unjustly in anything.) meaning, "We shall set up the Balances of justice on the Day of Resurrection.'' The majority of scholars state that it is one Balance, and the plural form is used here to reflect the large number of deeds which will be weighed therein.
("O my son! If it be equal to the weight of a grain of mustard seed, and though it be in a rock, or in the heavens or in the earth, Allah will bring it forth. Verily, Allah is Subtle, Well-Aware.'') 31:16 In the Two Sahihs it was recorded that Abu Hurayrah said that the Messenger of Allah said:
(Two words which are light on the tongue, heavy in the Balance and beloved to Ar-Rahman: "Subhan Allahi wa bi hamdihi, Subhan Allahil `Azim (Glory and praise be to Allah, Glory be to Allah the Almighty).'') Imam Ahmad also recorded that `A'ishah said that one of the Companions of the Messenger of Allah sat down before him and said, "O Messenger of Allah, I have two slaves who lie to me, betray me and disobey me, and I hit them and insult them. How do I stand with regard to them'' The Messenger of Allah said:
(The extent to which they betrayed you, disobeyed you and lied to you will be measured against the punishment you meted out to them. If your punishment was commensurate with their misconduct, then you will be equal and you will not have anything counted for you or against you. If your punishment of them was less than that what they deserved for their misconduct, then this will count in your favor. If your punishment of them was more than what they deserved for their misconduct, then Allah will take what is due to them from you.) Then the man started to weep before the Messenger of Allah, and the Messenger of Allah asked,
(What is the matter with him Has he not read the words of Allah, (And We shall set up Balances of justice on the Day of Resurrection, then none will be dealt with unjustly in anything. And if there be the weight of a mustard seed, We will bring it. And sufficient are We to take account.)) The man said, "O Messenger of Allah, I think there is nothing better than keeping away from these people -- meaning his slaves -- I call upon you to bear witness that they are all free.''
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
See also vv. 8-9 and E.N.'s 8-9 of Al-A'araf (Vll). It is difficult for us to understand the exact nature of the "Balance". Anyhow it is clear that the "Balance" will weigh accurately all the human moral deeds instead of material things, and will help judge whether a man is virtuous or wicked and how much. The Qur'an has used this word to make mankind understand that every deed, good or bad, will be weighed and judged according to merit.