According to the Qur’an, denying a Messenger of God in spite of being convinced about his veracity is something which deserves severe punishment both in this world and in the Hereafter since this is tantamount to deliberately denying the Almighty Himself. The worldly punishment of the Disbelievers (Kuffar) was carried out by the Almighty in two ways: Either He directly destroyed them Himself through disasters and calamities or by His Messengers and their Companions (rta) -- who in this exercise were no more than agents of His retribution. In the second case, the Messengers and their Companions (rta) just replaced the weapons of destruction as the role of earthquakes, storms, cyclones and lightning was assumed by them.
Referring to the first form of punishment, the Qur’an says:
Each one of them We seized for their crime: of them, against some We sent a violent tornado with showers of stones; some were caught by a mighty blast; some We sunk in the earth; and some We drowned in the waters. (29:40)
Referring to the second form of divine punishment,
the Qur’an asserts:
Fight them [ O Believers!] and God will punish them with your hands and humiliate them and help you to victory over them. (9:14)
While explaining this verse, the celebrated Muslim authority, Shah Wali Ullah, writes:It is not you [O believers] who slew them; it was [ in fact] God [who slew] them. (8:17)
In other words, what needs to be understood is that it was the Almighty who took matters in His own hands and punished the Kuffar in this world in the time of His Messengers. It is precisely for this reason that in this particular sphere, the Prophet Muhammad (sws) is not a role model for Muslims. What mankind needs to learn from this whole exercise is to be mindful of a reality that it tends to forget: reward and punishment in the Hereafter on the basis of a person’s deeds. This reward and punishment which is to take place in the Hereafter is substantiated visually by the Almighty through the agency of His Messengers so that mankind may always remain heedful to this reality. The court of justice which will be set up for every person on the Day of Judgement was set up for the nations of Messengers in this world so that the latter could become a visual testimony to the former. The Qur’an at numerous instances has used this argument to substantiate the reward and punishment in the Hereafter. In Surah Haqqah, for example, it says:The Prophet Muhammad (sws) and his Companions (rta) in the fulfillment of this mission became like angels who also strive for the implementation of God’s directives. The difference between angelic and human undertakings is that the former strive without being guided by any universal principle, while human beings fight for the sake of a definite overall objective given to them by the Almighty. Thus Jihad becomes the greatest of all their deeds. That is why the act of killing is not attributed to them. It is attributed to the Divine Being who issued the directive to kill. This is like ascribing the act of killing of a traitor to the ruler rather than the slayer, as the Qur’an says: ‘You slew them not, but God slew them’.6
The justification of the retribution carried out by the Messengers on the Kuffar is that through divine help, the basic truths7 become manifest in their personalities to the extent that no one is left with any excuse to deny it. In the words of the Qur’an, this is called Shahadah ‘ala al-nas (bearing witness to the truth before other peoples). The Almighty has referred to this aspect in the following words:The Inevitable! What is the Inevitable? What do you know what the Inevitable is? It is the Pounding One which the ‘Ad and the Thamud denied. As for the Thamud, they were destroyed by a calamity that exceeded all bounds and the ‘Ad by a storm, fierce and violent. He let loose this [storm] on them for seven nights and eight days to ravage them. You would have seen them lying overthrown as though they were hollow trunks of palm-trees. So do you now see any of them? And the same crime was committed by Pharaoh and those before him and by the overturned settlements also such that they disobeyed the Messenger of their Lord [sws]. So He gripped them with an intensifying grip. [Similarly, as a consequence of denying Noah (sws)] when [the storm blew over and] the flood rose high it was We who carried you upon the ark to make this [account of your ancestors] a reminder for you and that retaining ears may retain it . (69:1-12)
In other words, what authorizes a Messenger to punish the Kuffar is that it can be ascertained in this very world that they are guilty of denying the basic truths in spite of being convinced about them. Good and evil are elucidated with ultimate clarity and people who accept evil do so not because of any confusion but because of their own stubbornness.To you [O People of the Quraysh!] We have sent forth a Rasul as witness to the truth upon you just as we sent a Rasul to the Pharaoh. (73:15)
So it can be concluded that since a Messenger reveals the basic truths in their ultimate form and those who deny it do so because of their stubbornness and even confess their sins, a Messenger has the perfect justification to punish his people after they have denied him.