He was sent as a mercy to the worlds because he came with what makes them happy if they follow him. As for those who oppose and do not follow, they have only brought it upon themselves, as they have wasted their share of it. An example of this is that Allah may cause a spring to gush forth, so people water their crops and livestock with its water and prosper, while others neglect to water and thus suffer loss. The spring that gushes forth in itself is a blessing from Allah and a mercy for both groups, but the lazy one is a trial upon himself, as he has deprived himself of what benefits him. It is said that his being a mercy for the wicked is because their punishment has been delayed because of him, and they are safe from the punishment of annihilation.