Stated here is the real reason of their mischief. Imām Amīn Aḥsan Iṣlāḥī writes:
The actual words are: اَنْ تُبْسَلَ نَفْسٌۣ. A word to the effect مخافة (lest) is suppressed beforeاَنۡ in accordance with linguistic principles.
The actual words are: لَهُمْ شَرَابٌ مِّنْ حَمِيْمٍ وَّعَذَابٌ اَلِيْمٌۣ. In other words, their first feast will be boiling water and then they will be consigned to a severe torment. This has been specified by the Qur’ān in verse 93 of Sūrah al-Wāqi‘ah.
Tafsir Qur'an Wiki:
This verse re-emphasizes the distinction between the two communities, making several important points.
The Prophet, and indeed every Muslim, is commanded to ignore, by word and deed, those who treat religion as a pastime and as idle play. This description applies to anyone who does not give his faith respect by making it the basis of all aspects of his life: worship, beliefs, practices, moral values, and a legal code. It also applies to anyone who describes the principles and legislations of this faith in derogatory terms, such as those who ridicule the concept of believing in the world beyond the reach of human perception, which is an essential part of the Islamic faith. The same is the case with people who talk disrespectfully of zakat which is one of the pillars upon which the structure of Islam is built, or describe morality and chastity as the values of rural and feudal societies, and those who speak disapprovingly of the Islamic rules of marriage, or describe as fetters the sort of guarantees God has given to Muslim women to help them maintain their chastity. It applies above all to those who deny God’s absolute sovereignty and His authority to legislate for human life in political, social, economic and legal fields, claiming that human beings may legislate for themselves without reference to God’s law. All those are included as ones who `take their religion for a pastime and a sport’. Every Muslim is commanded to stay away from them except to remind them of their duty towards God. They are among the wrongdoers and unbelievers described in this verse as ones who are held in pledge for what they have done’. They are threatened with having to drink boiling water and having to endure painful suffering for their disbelief.
The Prophet, and indeed every Muslim is further instructed to remind these people of God and warn them against being held in pledge and destroyed in consequence of what they have done. They are to be reminded that they cannot enjoy any support against God, and no one can intercede with Him on their behalf. No ransom will be accepted from them. The Qur’anic style here is exceedingly beautiful and effective: “Remind them with this (Qur’an), lest every human being should be held in pledge for whatever he has done, when he shall have none to protect him from God, and none to intercede for him. If he were to offer any conceivable ransom, it shall not be accepted from him.” Every single soul will have to account for itself, without support, and when no ransom is of any use.
As for those who have taken their religion in jest and been beguiled by the life of this world, they are already held in pledge for what they have done. Their doom is sealed: “Those are the ones who are held in pledge for what they have done. Scalding water shall they drink, and grievous suffering awaits them because they were unbelievers.” The scalding water, which boils in their throats and stomachs, and the painful suffering which ensues are a fitting recompense for their ridicule of faith.
Speaking of the unbelievers, God describes them as "Those who take their religion for a pastime and a sport". Is it truly their religion? This description fits perfectly those who declared their acceptance of Islam and then treated their religion as an object of ridicule. There were some people like that to whom the appellation `hypocrites’ was given, but they were in Madinah. Can the same statement apply to unbelievers who did not embrace Islam in the first place? Well, Islam is the religion of all mankind, including those who do not believe in it, since it is the only faith God accepts from human beings ever since the revelation of the message preached by the Prophet Muhammad, the last of all messengers. Hence, anyone who rejects it actually rejects his own faith.
Hence, it is significant that the possessive pronoun is used in the beginning of this verse: “Stay away from those who take their religion for a pastime and a sport.” It is most probably, and God knows best, a reference to the fact that Islam is a religion for all mankind. Whoever makes fun of it, even though he may be an idolater, actually makes fun of his own religion. We probably still need to explain who are meant by the term `idolaters. They are those who claim that any being has a share of God’s attributes. This may take the form of believing in the existence of deities other than God, or offering worship and performing rituals to anyone other than God, or acknowledging the authority to legislate to anyone besides God. Needless to say, the term idolaters also include those who claim for themselves any of these, however strongly they may profess to be Muslims. We should then be clear about who belongs to our faith.
The last point concerns the limits within which it is permissible to sit with the wrongdoers, or idolaters, and those who take religion as an object of fun and ridicule. As we have already mentioned, this is permissible only when it is done to remind them of divine faith and to warn them against disobeying God. It can have no other purpose. Once we realize that they engage in idle talk about God’s revelations or treat them as an object of ridicule we must leave their company immediately. In commenting on this verse, al-Qurtubi explains the rulings mentioned in the Qur’an: “This verse provides an answer in God’s Book to anyone who claims that high standing Imams and their followers may have social contacts with wrongdoers, or may try to protect themselves by pretending to accept their views as correct.”
Our view is that the Qur’anic verse allows mixing with the wrongdoers in order to admonish and warn them, and to correct their erring views. Mixing with them and keeping quiet about what they say and do in order to protect ourselves is unacceptable, because it imparts an impression of accepting falsehood and rejecting the truth. In addition, it deceives people and degrades the divine faith and its advocates. Such a situation is totally unacceptable.