In these series of articles we focus on verses that are intended to say something about Imam Mahdi who is the Last Savior.
God in surah al-Hajj, verse 39 states, “Permission to fight is issued for those believers who were oppressed by the disbelievers and certainly Allah is Powerful to aid the oppressed believers.” «أُذِنَ لِلَّذينَ يُقاتَلُونَ بِأَنَّهُمْ ظُلِمُوا وَ إِنَّ اللَّهَ عَلى نَصْرِهِمْ لَقَديرٌ»
It is narrated form Imam Saadiq (the Shiite sixth Imam) who explains this verse and says,
عَنْ أَبِي عَبْدِ اللَّهِ ع فِي قَوْلِهِ أُذِنَ لِلَّذِينَ يُقاتَلُونَ بِأَنَّهُمْ ظُلِمُوا وَ إِنَّ اللَّهَ عَلى نَصْرِهِمْ لَقَدِيرٌ قَالَ إِنَّ الْعَامَّةَ يَقُولُونَ نَزَلَتْ فِي رَسُولِ اللَّهِ ص لَمَّا أَخْرَجَتْهُ قُرَيْشٌ مِنْ مَكَّةَ وَ إِنَّمَا هُوَ الْقَائِمُ ع إِذَا خَرَجَ يَطْلُبُ بِدَمِ الْحُسَيْنِ ع
“Sunnis (at the age of the Prophet) believed that this verse was revealed to mean the Prophet who was forced to live Mecca by the Quraish tribe in there, but (the more important example of it is that) it points to the Upriser (Imam Mahdi) that, when he comes he will seek the revenge for Imam Hussein’s blood (who is the Shiite third Imam.)”
This verse with the mentioned narration contains some considerable points:
The revenge for those who are oppressed will be taken: The blood of those who were the friends of God and were killed in His path will never be dismissed by God. This world will never come to an end by the oppressors being left victorious. The disbelievers are those who used all of the available worldly blessings of God but not only did not respect God, also killed and oppressed those who were the friends of God and were the assistants of His religion.
God will help Imam Mahdi to seek revenge: When the Imam appears that this the time the issue of taking revenge will be issued God also will help him. This is what God says at the end of the verse at hand that certainly Allah is Powerful to aid the oppressed believers. It is clear that those who are supported by God will be victorious even if those who oppose are more in number and possess more war equipment.
The blood of Imam Hussein is a symbol of those who were oppressed: The mentioned narration although refers to the blood of Imam Hussein but this is an example for the most important incident took place between the pious and the evil doers. Therefore, to seek the revenge for the blood of Imam Hussein means to seek the revenge for those who has done the same like those who killed him. Imam Hussein was killed to save the religion of God and to put an end to innovation and oppression. As a result, those who are against this philosophy are like those who opposes and killed him and Imam Mahdi will oppose all of them. Here, since God promises to help the Imam, it means that God is actually who decides to seek the revenge. It also indicates that the defeat of those who oppose God will start from this world.
 Bihaar al-Anwaar, v. 51, p. 47, hadith 7.