اعْدِلُوا هُوَ أَقْرَبُ لِلتَّقْوَىٰ
I‘dilū huwa aqrabu lit-taqwā
Be just, that is closer to piety (Sūratul Mā’idah, No. 5, Āyat 8)
There are few things as important as the concept of justice in Islam. Justice, like the oneness of God, pervades all roots and branches of religion. According to Tafsīr-e Namūne, just as all beliefs and actions, individual and social, are meaningless without the belief in the oneness of God, they are also meaningless without the spirit of justice.
Justice is the goal of all Divine revelations and is at the heart of the messages brought by the Messengers. It is a trust and responsibility, and has to be fulfilled. Justice in society creates balance and equilibrium. It is not just human society that cannot function without justice. The entire system of Allah is based on justice, or putting things in their rightful place. Thus without justice, there is imbalance and chaos.
Āyatullah Shahīd Mutahharīin his book Divine Justice describes justice in four different ways:
1) Balance – the sum parts of a total should be as required, not necessarily equal.
2) Non-discrimination -the application of equality based on equal merit.
3) Rights – giving to each it’s due, not withholding or transgressing the rights of others.
4) Bestowal of existence and perfection based on merit. This is the attribute of Justice that is worthy of God.
Justice in Hadīth has been described as: an ornament of faith (MH, H.11682), sweeter than water received by a thirsty person (MH, H.11660), and better than worship of seventy years (MH, H.11673). Imam Amīrul Mu’minīn Ali (a) was asked what was better, justice or generosity. He replied; Justice puts things in their proper place and generosity diverts them from their (natural) direction. Justice is the general caretaker, whereas generosity is a particular reliever. Thus justice is the nobler of the two. (MH, H.11681)
To be just to others and fulfill their rights is an essential of faith, stemming from the belief in a just God.
Sources: http://enconf.motahari.ir/images/file/pdf/What_is_Justice_8764.pdf
Aytaullāh Nāsir Makārim Shirazī (ed.), Tafsīr Namūne; MuhammadīRayshahrī, Mizānul Hikmah.