This Surah is called Nun as well as Al-Qalam, the words with which it begins.
This too is one of the earliest surahs to be revealed at Makkah, but its subject matter shows that it was sent down at the time when opposition to the Holy Prophet (upon whom be peace) had grown very harsh and tyrannical.
It consists of three themes: Replies to the opponents objections, administration of warning and admonition to them, and exhortation to the Holy Prophet (upon whom be peace) to patience and constancy.
At the outset, the Holy Prophet has been addressed, to the effect: "The disbelievers call you a madman whereas the Book that you are presenting and the sublime conduct that you practice, are by themselves sufficient to refute their false accusations. Soon they will see as to who was mad and who was sane; therefore, do not at all yield to the din of opposition being kicked up against you, for all this is actually meant to cow you and make you resort to a compromise with them."
Then, in order to enlighten the common people the character of a prominent man from among the opponents, whom the people of Makkah fully well recognized, has been presented, without naming him:At that time, the Holy Prophet's pure and sublime conduct was before them, and every discerning eye could also see what sort of character and morals were possessed by the chiefs of Makkah, who were leading the opposition against him.
Then, in vv. 17-33, the parable of the owners of a garden has been presented, who after having been blessed by Allah turned ungrateful to Him, and did not heed the admonition of the best man among them when it was given them. Consequently, they were deprived of the blessing and they realized this, when all they had lay devastated. With this parable the people of Makkah have been warned to the effect:"With the appointment of the Holy Prophet (upon whom be peace) to Prophethood, you, O people of Makkah, too, have been put to a test similar to the one to which the owners of the garden had been put. If you do not listen to him, you too will be afflicted with a punishment in the world, and the punishment of the Hereafter is far greater."
Then, in vv. 34-47 continuously, the disbelievers have been admonished, in which the address sometimes turns to them directly and sometimes they are warned through the Holy Prophet (upon whom be peace). A summary of what has been said in this regard, is this: Well being in the Hereafter inevitably belongs to those who spend their lives in the world in full consciousness of God. It is utterly against reason that the obedient servants should meet in the Hereafter the same fate as the guilty. There is absolutely no basis of the disbelievers misunderstanding that God will treat them in the manner they choose for themselves, whereas they have no guarantee for this. Those who are being called upon to bow before God in the world and they refuse to do so, would be unable to prostrate themselves on the Day of Resurrection even if they wanted to do so, and thus would stand disgraced and condemned. Having denied the Qur'an they cannot escape Divine punishment. The rein they are being given, has deluded them. They think that since they are not being punished in spite of their denial, they must be on the right path, whereas they are following the path of ruin. They have no reasonable ground for opposing the Messenger, for he is a preacher without any vested interest: he is not asking any reward of them for himself, and they cannot either make the claim that they know with certainty that he is not a true Messenger, nor that what he says is false.
In conclusion, the Holy Prophet (upon whom be peace) has been exhorted to the effect:"Bear with patience the hardships that you may have to face in the way of preaching the Faith till Allah's judgment arrives, and avoid the impatience which caused suffering and affliction to the Prophet Jonah (peace be on him)."
Source: Sayyid Abul Ala Maududi - Tafhim al-Qur'an - The Meaning of the Quran