He warned the disbelievers by reminding them of the hereafter

one of the most prominent characteristics of those who deny allah is that they do not believe in the hereafter. in the time of the prophet (saas) too, such people would not believe that people would be resurrected in the hereafter. the prophet (saas) responded to their claims with the wisest and most concise answers. the prophet (saas) was commanded to employ such language in the qur'an:

they say, "what! when we are bones and crumbled dust, will we then be raised up as a new creation!" say: "it would not matter if you were rock or iron or indeed any created thing that you think is harder still!" they will say, "who will bring us back again?" say: "he who brought you into being in the first place." they will shake their heads at you and ask, "when will it happen?" say: "it may well be that it is very near." (surat al-isra': 49-51)

"when we are dead and turned to dust and bones will we then be raised up again alive? and our earlier ancestors as well?" say: "yes, and you will be in a despicable state." (surat as-saffat: 16-18)

in the hope that they would turn to the true path and believe, the prophet (saas) told them that the hereafter is not far off:

"paradise is nearer to any of you than the strap of his shoe, and so is the (hell) fire."62