(O Muhammad!) We have sent you to be a real blessing for the people of the world. Say to them, “That which is revealed to me is this: Your Deity is One Deity only. Will you, then, surrender to Him?” If even then, they turn away from it, tell them plainly, ‘I have warned you openly; now I do not know whether that thing with which you are being threatened is near at hand or far off. You should, however, note it well that Allah has the knowledge of what is uttered aloud and also of what you talk about secretly’.”
(Al-Qur’ān – 21:107-10)
Muhammad ﷺwas Allah’s Messenger for all human beings. The Qur’ān asserts he was sent as a “real blessing” for all people. The appointment of the Messenger was indeed a blessing and mercy of Allah to the whole world. This is because he awakened the neglectful world from its heedlessness and gave it the knowledge of the criterion between truth and falsehood and warned it very clearly of both the ways of salvation and ruin.
This is to tell disbelievers that they were quite wrong in their estimate of the Holy Messenger that he was an affliction and distress for them.
The expression, “I do not know whether that thing with which you are being threatened is near at hand or far off” means: “I do not know the time and the form of the punishment of Allah for your rejection of the Message. It may come at any time in any shape.”