The aim of creating the entire universe is perfection and getting closer to the source of all perfections, Almighty God. To fulfill this aim some tools should be available. Imam Mahdi (p.b.u.h.) tries to establish a reign which helps people achieve this final destination and removes obstacles.
Human being uses of two dimensions: body and soul. So his needs are both material and spiritual. To prepare both of them, there should be a studied and prudent plan, and “justice”, which is the result of God’s rule over the world, is a full guarantee on fulfillment of these needs toward perfection.
Therefore, Imam Mahdi (p.b.u.h.)’s reign and its aims toward justice and developing it, can be studied in two parts: spiritual growth and developing and fulfillment of justice.

1. Spiritual Growth
When we look back in the history, we find the man facing difficulties and being for from salvation.
Spirituality and virtues have been vanished and through centuries of devil reign over the world, human being has lost his destination. He moved in the wrong way toward evil and desires so that all beauties of his heart and soul faded. He forgot his high position and buried his soul in the graveyard of devil. He changed purity, honesty, trustworthiness, self – sacrifice, chastity, generosity, cooperation, helping others, and all virtues with lust, lies, deceitfulness, crime, self – centeredness, dishonesty, greed, ambition, and all impurities. In other words, Spirituality is dying and in most of so – called “human beings” there is nothing left but sin.
Imam Mahdi (p.b.u.h.) comes back to revive that dying part of our souls. He will make us experience the sweet taste of real life. He will remind us the vow we made to God and the praise we received by angels. He will make us think again and give us clues to the right path. May God guide us all? Now it is our turn to follow and abbey him:
“O! you believers; answer the call of Allah and his Messenger, when he does call you to that which will give you life…”
when Imam Mahdi (p.b.u.h.) establishes his reign of justice, the spiritual aspects of our souls is going to be developed; for this part is the major part of our lives and to achieve our final destination, i.e. visiting Allah while being perfect and pure, he helps us and teaches us to be truly virtuous. Surely this needs a complete and specific plan which will be explained more in following parts.
2. Developing Justice
The greatest wound on the body of humanity is injustice and cruelty, which have always bothered the poor and weak societies. Sources and God’s gifts have never been divided fairly between people and most of people have always been deprived of their absolute rights. There are always some staring poor people, where at the same time some others eat like horses. Some wealthy people live in palaces, while some others sleep in the parks or sidewalks. The powerful exploit the weeks and enslave them and the white men whip the black men, just for being black. In other words, the powerful always violate the weak’ rights and the world whishes to see the day when there is no injustice, nor cruelty.
This awaiting for justice shall be ended when Imam Mahdi (p.b.u.h.) comes back. He is always named as the just leader and fair ruler. As Imam Hussein (p.b.u.h.) says:
“I heard this from my grand father, the holy prophet (p.b.u.h.) that if remains nothing but just one day of this world, God shall make it longer until the time when a man of my offspring rises up and fills the world with justice as it is full of cruelty and injustice.”
According to this Hadith and many others, he will fill the world with justice, as his most important duty. This responsibility is so well know that “justice” is one of the titles of Imam Mahdi (p.b.u.h.). We see in prayers:
“Oh Lord! Praise holder of your word, who is the promised one, the one who shall rise up and the awaited justice.”
Therefore, as his most important goal, he brings justice to the world and then it revives the whole societies Imam Kazem (p.b.u.h.) says:
“In the verse: “Know that it’s Allah who revives the earth after it dies…” God does not mean that with rain he revives the earth; but He rises up some men who bring back the justice. Then with justice [in all the societies] the earth will be revived.
Therefore, when the earth is revived, we can conclude that Imam Mahdi (p.b.u.h.) fills the “whole” world with justice, not just parts of that and for some people..