Ma'arif al-Qur'an
Mufti Muhammad ShafiCommentaryمَن كَانَ يَظُنُّ (If someone thinks - 22:15). It means that the enemies of Islam who put hurdles in its path and desired that Allah should abandon the Holy Prophet ﷺ and his religion must clearly understand that this can happen only when, God forbid, he is deprived of the office of the prophethood and ceases to receive wahy (revelations) from Allah Ta’ ala. It is well understood that when Allah Ta’ ala bestows the prophethood on someone and also favours him with wahy (revelations), He also promises him full support in this world and in the Hereafter. Thus the only way to stop the advancement of a prophet and his mission, if someone has the power to stop it, is that he should dispossess the Holy Prophet ﷺ of his mission or that the sequence of Divine revelation should be severed. Anyone wanting to do all this will have to go up to the sky and cut off the chain of revelation, and since such a thing is not possible, no amount of fire and fury can do any harm to Islam.
This interpretation is related in al-Durr al-Manthur from Ibn Zaid and, in my opinion, it is the most appropriate one.
Qurtubi also thinks that this is the best interpretation of this verse. There are some others who are of the view that the word سَمَاء (sky) occurring in this verse means the ceiling of one's house and the verse means that a person who entertains hostile feelings towards Islam and the Holy Prophet ﷺ must realize that he can do them no harm. Hence the best thing for him to do is to hang himself from the ceiling out of sheer mortification. (Mazhari and others).