Those who reject the Signs of Allah and the Meeting with Him (in the Hereafter),- it is they who shall despair of My Mercy: it is they(3443) who will (suffer) a most grievous Penalty.
3443 The emphasis is on "they" (ula'ika). It is only the people who ignore or reject Allah's signs and reject a Hereafter, that will find themselves in dispair and suffering. Allah's mercy is open to all, but if any reject His Mercy, they must suffer.