وَنَضَعُ ٱلْمَوَٰزِينَ ٱلْقِسْطَ لِيَوْمِ ٱلْقِيَـٰمَةِ فَلَا تُظْلَمُ نَفْسٌ شَيْـًٔا ۖ وَإِن كَانَ مِثْقَالَ حَبَّةٍ مِّنْ خَرْدَلٍ أَتَيْنَا بِهَا ۗ وَكَفَىٰ بِنَا حَـٰسِبِينَ

In the present world, a ‘balance (or scale)’ is a device for finding out the weight of an object. Therefore, God has used this known term to explain the events on Judgement Day. Where the scales of the world weigh material things, on the Day of Judgement, the scales of God will weigh intangible facts and show their ‘weights.’ That is, the scales of the world can measure the material aspect of things but the divine scales will be able to measure the inner value of our deeds. In this world, a man obtains things by paying for them. One who pays less receives less and one who pays more receives more. The same will be the position on the Day of Judgement. Things of high value will be available only on payment of their price which will be in terms of good deeds. Just as things are not available gratis in this world, similarly things will be available on the Day of Judgement only on making a suitable payment: the Quran is a book which indicates what the cost will be. According to the Quranic criterion, a believer will have to develop a spiritual personality in this world itself. This is the price which he has to pay if he wants to find an entry into the ideal world of Paradise.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (21:47)