Similar to how you have worded your question, it is best that we begin by seeing if the verses of the Holy Quran talk solely about painful punishment, or do they rather discuss other aspects as well? From thereon we will follow up on the topic of punishment, its effects, and the view one can find towards the one who punishes. Truly, for one who punishes, can anything but unkindness and cruelty be expected?
As you may already be aware, the Holy Quran includes many verses with different words and phrases all pointing to Allah's (SWT) pervasive mercy. Words like Rahman (referring to Allah's (SWT) general mercy), Rahim (referring to Allah's (SWT) special mercy), Arham al-Rahimin (the most gracious), Ra'ouf (kind), Wadood (affectionate), and many more all fall under this category of Allah's mercy.
Usually the most important and dominant concepts of a school of thought can be found in its title or slogan. One of the most important slogans in Islam is "Bismillah al-Rahman al-Rahim" (In the Name of Allah, the Compassionate, the Merciful). Muslims usually begin their daily activities and work with this phrase. In addition, with the exception of one chapter, all chapters in the Holy Quran begin with this phrase. Allah (SWT) has various names and titles; however it is very interesting that from amongst all these names (1), the titles Rahman (Compassionate) and Rahim (Merciful) are specifically chosen for praising Him. Moreover Muslims refer to Allah's (SWT) mercy as they call Him with these two titles at least 60 times a day in their daily prayers.
Allah's (SWT) mercy in the Holy Quran
Other than the times the word Compassionate (Rahman), has come in the phrase "Bismillah al-Rahman al-Rahim", the word Rahman has been mentioned forty one times and the word Merciful (Rahim) can be seen eighty other times.
Taking a look at the other verses of the Holy Quran will introduce us to other insights regarding the mercy of Allah (SWT). One verse explicitly states that Allah (SWT) has made mercy obligatory upon Himself: "
your Lord has ordained mercy on Himself
" (2) However, such a verse cannot be seen about His wrath. The Holy Quran even includes different examples where Allah (SWT) has forgiven people through His pervasive mercy, even though they had not asked for forgiveness. The Holy Quran presents Allah's (SWT) immense mercy to such an extent that other than the great sin of polytheism, all other sins may be forgiven: "(Surely) Allah does not (ever) forgive that anything should be associated with Him (polytheism), and forgives what is less than that to whomsoever (He pleases and believes worthy)
Allah's (SWT) mercy from the beginning of creation to the end of creation
When the Holy Quran presents the beginning of human creation, it declares Allah's (SWT) mercy as the reason of creation:"
Except those on whom your Lord has mercy on; and for this (acceptance of mercy) He created them
" (4) Similarly, the mercy of Allah is again reminded when the end of the world and the resurrection day is discussed: "Say: To whom belongs what is in the heavens and the earth? Say: To Allah; He has ordained mercy (and forgiveness) on Himself; (and for this reason) certainly He will gather you on the resurrection day, there is no doubt about it
Therefore, it is obvious that in introducing Allah (SWT) to the non-believers, the Holy Quran refers to Allah's mercy before all else, and describes Him as the owner of pervasive mercy: "But if they accuse you of falsehood (and don't accept these facts), then say: Your Lord is the Lord of All-encompassing mercy
No disappointment whatsoever
The Holy Quran describes this mercy to be so vast that only the misled people lose hope. Quoting Prophet Ibrahim (Abraham) (PBUH), the Quran says: "And who despairs of the mercy of his Lord but those who are astray!?" (7) Despite all their sins and disobediences, Allah (SWT) continues to call them His servants, telling them not to lose hope in His mercy for He is all-forgiving: "Say: O my servants who have acted extravagantly and oppressively against their own souls! Do not despair of the mercy of Allah; surely Allah forgives all the sins, because He is Forgiving and Merciful". (8)
Examples of Allah's (SWT) mercy
Allah's (SWT) forgiveness; a unique mercy:
Do you know the true definition of Allah's (SWT) forgiveness (Safh), which is named as one of His characteristics? We, as humans, may have disobeyed an authority during our lives. Supposing that he has forgiven us and treated us with kindness, naturally any time we meet him, we would remember the incident and feel some shame. If that person is extremely kind, he will forget about our disobedience; however, he cannot make us forget our fault, nor can he stop us from feeling shameful. Allah (SWT) however, is indeed different. Although He does not forget anything, He makes it so that we forget our disobedience and do not feel any embarrassment. This is what Allah's (SWT) forgiveness (Safh) means
If so much mercy, so why torture?
If Allah (SWT) has so much mercy, then why did He create Hell? Why has He talked about its tortures in the Holy Quran? Does it mean that although creating heaven originates from Allahs (SWT) mercy, He has neglected His mercy when creating Hell?
If we refer to the teachings of Ahl al-Bayt (PBUT) for these aspects, we will come to surprising statements. Our Imams (PBUT) have taught us that Allah's (SWT) mercy precedes His wrath (11). Moreover, in a phrase of Sahifah Sajjadiah (12), Imam Sajjad (PBUH) addresses Allah (SWT) through the following: "O my Lord! You are the one whose mercy precedes His wrath (13)".
Looking carefully into this precious statement, we understand that Imam Sajjad (PBUH) is teaching us that Allah's (SWT) wrath is controlled by His mercy, meaning that His anger originates from His mercy.
According to the monotheistic thoughts, Allah (SWT) is free from all needs; thus, our sins and disobedience neither benefits nor harms Him. Therefore, the divine obligations and prohibitions are for our own benefits, and are in fact means for our accomplishment. The instructions, programs, and methods He has sent us through His messengers are all based on His mercy. If we commit ourselves to these instructions, we will achieve accomplishment; otherwise, we will not gain anything but loss.
Allah's (SWT) warnings, a sight of His mercy:
But Allah (SWT) did not suffice to only sending orders, but rather placed rewards for obeying Him, and punishment for not obeying Him.
Allah's (SWT) purpose of punishment is different from the punishment carried out by the human beings, in that Allah's punishments are not out of fun or revenge. The Holy Quran states that even the creation of Hell derives from Allah's mercy. If the hell did not exist and people did not fear its torture, many people would not have the motivation to move in the path of accomplishment and would not turn away from corruption. Thus even the Hellfire in itself is a result of Allah's (SWT) mercy. If Allah (SWT) had not created the Hellfire, and if we had been assured that no torture existed, Allah's (SWT) warnings would have become useless and many people would have freely remained misled.
In order to further clarify this subject, let us look into the following example. A doctor who has a sick son realizes that he must remove the harmful tumor from his son's body. When the father uses a knife and cuts his son's body, does he do such out of anger, want of money and fame, or does he do such out of his fatherly love and affection toward his son?
The same thing is true about Allah (SWT). Considering the fact that He does not need our obedience, and that our disobedience does not hurt Him, wouldn't the creation of Hell originate from nothing but mercy?
The origin of punishment in the hereafter
In addition, many of the divine warnings for the punishments are to inform us of the essence and truth of our own deeds. The Holy Quran clearly notifies us of this fact; for instance, when a person usurps an orphan's property, the essence of his act is nothing but fire. In fact, he is eating fire (14), but he does not feel its heat because he is like a person who is not conscious. He will however feel and recognize the fire on the Day of Judgment.
Therefore, in the Holy Quran, Allah (SWT) informs us about the validity of our deeds, and warns us about their results. This is similar to telling someone that excess in eating can result in a stomach ache. Our body has been designed in such a way that overeating can result in a stomach ache. The same thing is true about our souls: committing sins results in undesirable influences upon our souls. A few recognize the influence right away, whereas others may recognize them after awhile.
Thus, Allah (SWT) has only informed us about the natural laws that run in this world.
Oppression and assault, what is our Duty?
The question yet remains as to what our duty is towards those who abuse the rights of other people. Do the kindest people admire such people for their oppression or do they reproach and punish them? After all, how do the most democratic governments treat those who have recurrently committed crimes, and have overlooked all kinds of mercy and kindness? How do communities prevent people from abusing the rights of others? Is there any way other than punishment and chastisement?
Therefore, punishing the abusers is a wise, humane, and innate issue, which has deterrent influences as well. Allah's (SWT) wrath has the same rationale. If it was not because of Allah's (SWT) warning of punishment, then how could one control his/her desire from abusing the rights of others?
The creation of Hell therefore does in fact originate from the mercy of Allah (SWT). He warns us of our wrongdoings and through the divine punishment prevents people from abusing each other's rights.