Tafsir of Al-Anbiya' 21:107

"And We have not sent you, [O Muhammad], except as a mercy to the worlds."

He (peace be upon him) was sent as a "mercy to the worlds" because he brought that which would bring them happiness if they followed him. As for the one who opposes and does not follow, the harm comes only from his own self, for he has squandered his share of that mercy.

The Parable: It is like God causing a bountiful spring to gush forth. Some people use its water to irrigate their crops and livestock, and thus they prosper. Others are negligent and fail to irrigate, and thus they perish. The spring itself is, in its essence, a blessing from God and a mercy to both groups. However, the lazy person becomes a trial for his own self, as he deprives it of what would benefit it.

Another View: It is said that his being a mercy to the wicked lies in the fact that their punishment was delayed because of him, and they were secured through him from the torment of total annihilation.

"Say, 'It is only revealed to me that your god is but one God; so will you be Muslims [submitting to Him]?'"