" Allah does not like the saying of evil words openly except from anyone wronged. And Allah is All-Hearing, All-Knowing. 
If you do good openly or keep it secret or overlook an evil deed, then, Allah is All-Forgiving, All-Powerful. 
Surely those who disbelieve in Allah and His Messengers, and wish to make division between Allah and His Messengers, and say, "We believe in some and disbelieve in some others" and wish to take a way in between that. 
Those are the disbelievers in reality, and We have prepared for the disbelievers a humiliating punishment. 
And those who have believed in Allah and His Messengers, and have made no division between any of them, to them He will give their rewards. And Allah is Most-Forgiving, Very-Merciful." (4:148-152)
Out of these verses, the first (148) and the second (149) give a law to eradicate injustice and oppression from the world. But, this is not like the usual worldly laws which are limited to dictatory formulations. This, in turn, is the kind of law which tries a combination of persuasion and awe whereby, on the one hand, the victim of injustice has been permitted to protest against the perpetrator of injustice, or to go to a court of law to seek redress. All this is nothing but the basic demand of justice and, certainly, a source of eradication of crimes. But, along with this option, there is a restriction on it as mentioned in Surah al-Nahl: It means: 'If a person inflicts injustice on you, you too can retaliate against him for that injustice. But, the condition is that your retaliation should not exceed the unjust aggressive action by him - if so, it is you who would turn into the unjust one.' (16:126) The outcome is that returning an injustice by another injustice is not allowed. Rather, the retaliation to injustice, if any, can be made only through justice. On the other hand alongwith this course of action, comes the instruction that revenge is, though permissible, yet observing patience (sabr) and forgiving is better.
This verse also tells us that for an oppressed person who goes about complaining to people about the injustice done to him or her, this will not be included under backbiting ghibah, which is haram (forbidden) - because it is the oppressor who has given the victim the opportunity to complain. Thus, the Holy Qur'an has, on the one hand, allowed the oppressed person to use the option of 'even retaliation' against the injustice. On the other hand, by teaching the oppressed to practice high morals and to forgive and forget, and by focusing before him the the great gain of the life-to-come, the victim of injustice has been persuaded to do a little sacrifice in this matter of his legitimate right and take no revenge for the injustice inflicted. The Holy Qur'an says: If you do good openly or keep it secret or overlook an evil deed, then, Allah is All-Forgiving, All-Powerful - 4:149
It means: If you do a good deed openly or do it secretly or forgive any injustice or evil done by someone, then, this is better, because Allah is All-Forgiving, All-Powerful. Primarily, this verse is concerned with the forgiving of injustice but, by also mentioning the doing of what is good, openly or secretly, the hint given is that this act of overlooking and forgiving is great and anyone who elects to do it shall become deserving of the mercy and forgiveness from Almighty Allah.
Towards the end of the verse, by saying (Allah is All-Forgiving, All-Powerful), it has been made clear that Allah is powerful in the absolute sense. He can punish whomsoever He wills, yet He is All-Forgiving. Now, a human being, who does not have much of power or choice, were to think of taking revenge, it is quite possible that he may just not have the capability to do that. Therefore, for such a person, overlooking and forgiving is far more desirable.
This is the principle which the Holy Qur'an enunciates to eradicate injustice and reform the society. The counsel, befitting of the Sustainer of everything, does, on the one hand permit retaliation in an equal measure, thus upholding justice. On the other hand, it exhorts the aggrieved party to forgive and forgo. The result is what has been described in Qur'an at another place: "You will see that he with whom you had enmity has become your closest friend" (41:34).
Court decisions and taking of revenge for injustices do play a role in checking injustice. The fact, however, is that the parties to the dispute are usually left saddled with long term grievances and feelings of abhorrence against each other which can result in further disputes in the future. The impeccable lesson in morality, given by Holy Qur'an, results in patch up among quarrelling parties such that even old enmities change into close and lasting friendships.
Now, we move on to verses 150, 151 and 152 where the Holy Qur'an has given the clear verdict that anyone who believes in Allah but does not believe in His messengers, or believes in some of them and does not believe in some others is not a believer in the sight of Allah. He is, rather, an open and avowed disbeliever for whom there is no road to salvation in the Hereafter. Let us examine this aspect of the verses concerned in some detail.
This clear verdict of the Holy Qur'an has exposed the rudderless and crooked ways of those who, in an effort to appear tolerant in dealings with peoples of other faiths, would like to present their religion and religious beliefs as gifts on a platter. By doing so, they wish to tell - despite and contrary to the clear injunctions of the Qur'an and Sunnah - people of other faiths that Muslims do not think that salvation depends on Islam alone and a Jew could keep to his or her creed and a Christian to his or hers and yet, both could look forward to salvation; though, they deny all prophets or at least some of them, for which reason this verse has declared them to be the kind of disbelievers who are destined for Hell.
There is no doubt about the fact that Islam stands unmatched in its attitude to non-Muslims in matters of justice and fairness, sympathy and goodwill, favour and tolerance. But, good favours can be made within the limits of one's rights and possessions. Religious principles and articles of faith are not our property which we could donate or present to somebody. Of course, Islam is generous and benevolent in its teachings of tolerance and good treatment with non-Muslims, but it is also equally cautious and firm in the defence of its frontiers. It maintains its essential approach of all possible sympathy and maximum tolerance with non-Muslims, but, at the same time, Islam absolves itself decisively from all forms of disbelief and customs woven around it, declaring Muslims as a people distinct from non-Muslims - and yet, it provides full protection to their national hallmarks. In short, Islam prefers to keep not only the acts of worship Muslims perform distinct from those of others, but also its way of life in a society, the examples of which abound in the Qur'an and Sunnah.
Had Islam believed in the possibility of salvation through every religion or community, it would have had no right to lay so much stress on spreading the message (Tabligh) of Islam, almost to the limit of staking property and life for it. This would have been wrong in principle and quite contrary to dictates of reason. In fact, by accepting such a premise, the very coming of the noble Prophet, may the blessings of Allah and peace be upon him, and the revelation of the glorious Qur'an, is rendered, God forbid, redundant. And, lest we miss, the entire Jihad carried out by the noble Prophet Sallallahu 'Alayhi Wasallam: Peace be upon him and the rightly-guided Caliphs (R.A) becomes meaningless, rather reduced to nothing but the lust for more land.
In this case, some people have fallen victims to doubt by a misreading of verse 62 in Surah al-Baqarah which is cited below:
Surely, those who believed in Allah, and those who happened to be Jews and Christians, and the Sabeans - whosoever believes in Allah and in the Last Day, and does good deeds - they have their reward with their Lord, And there is no fear for them nor shall they grieve.
Since, in this verse, rather than giving the full detail of what constitutes faith, only belief in Allah and in the Last Day has been considered sufficient, those who try to understand the Qur'an through an incomplete study have misunderstood the whole idea. They assumed that simply believing in Allah and the Last Day is enough for salvation and that believing in prophets is no condition for it. Thus, they failed to understand that the Qur'an has its own terminology in which Belief in Allah, in order to be acceptable, has to be in conjunction with Belief in the Prophet. Otherwise, even the Satan admits that there is a God and that He is One. The Holy Qur'an has Itself clarified the real issue in the following words:
So, if they believe in the like of what you believe in, they have certainly found the right path. And if they turn away, they are nothing but in antagonism. Then Allah will suffice you against them, and He is the All-Hearing, the All-Knowing. (2:137)
In other words, we can say that their faith will be valid and trustworthy only when they have the same faith as common Muslims do, a faith in which Belief in the Prophet is indispensably necessary with Belief in Allah. Otherwise, if they do not do that, let it be understood that they are the ones who wish to create dissension. After that, for them, Allah will be sufficient on your behalf, and He is the One who hears everything and He is the One who knows everything.
As for the verses under discussion, it has been clearly declared that anyone who rejects even one of the prophets of Allah is an avowed disbeliever (kafir) and a recipient of the punishment of Hell. So, let us remember that Belief in Allah, in order to be valid, has to be with Belief in the Prophet. If the Belief in the Prophet is not there, even referring to Belief in Allah as such will not be correct.
In the concluding verse (15:22), it has been reaffirmed that salvation in the Hereafter is the lot of those who believe in Him and in all of His prophets as well. Therefore, the Holy Prophet Sallallahu 'Alayhi Wasallam: Peace be upon him said:
One part of the Qur'an explains the other.
It is not permissible for anyone to explain the Qur'an in any way contrary to the Tafsir of the Qur'an itself. [Ma'ariful Qur'an]