Firstly...
Firstly, reference is made to the Noble Messenger of God (S) as “a Mercy bestowed upon the world,” since he tolerated all the polytheists’ persecutions and it is unknown whether he ever cursed them but it is known that he asked God Almighty to bestow forgiving upon them through His Mercy and Favor.
It is mentioned in the Qur’an: “Whether you [O Muhammad (S)!] ask forgiveness for them or ask not forgiveness for them [and even] if you ask seventy times for their forgiveness – Allah will not forgive them,” ^2 ).
Secondly, the afflictions other than jihad inflicted on disbelievers by Divine Command might have been inconsistent with his noble disposition since Quraysh disbelievers were his kith and kin and despite their dire persecutions he did not wish for their being afflicted by Divine torment; as a consequence of which he is told that when we take you from the world or when you emigrate from Mecca God Almighty will take vengeance of them which is confirmed by another Qur’anic Verse, “And Allah would not chastise them while you are amongst them” ^3 .
Verse 42 is a consolation for the Noble Prophet (S) according to which God Almighty will take vengeance of them following his demise or emigration from Mecca to Medina. It may also serve as a warning to Meccans to the effect that God Almighty will take His Messenger’s (S) vengeance of them in his lifetime in the Battle of Badr or at a later time. God Almighty is Omnipotent and may take vengeance of them at any time.
One who is on the Right Path benefiting from Divine Revelation is supposed to be assiduous and of lively disposition in his work: (“hold you fast”) and he is supposed to entertain doubts regarding his true beliefs because of people’s oppositions: (“Indeed you are on the Straight Path”). Addressing His Noble Prophet (S), God Almighty says unto him: “O Muhammad (S)!