The surah takes its name, Al-Mu'minun, from the first verse.
Both its style and theme indicate that it was revealed during the middle stage of Prophethood at Makkah. Reading between the lines, one feels that a bitter conflict had begun between the, Holy Prophet and the disbelievers of Makkah, though the persecution by them had not yet become tyrannical. It appears that the surah was sent down during the climax of the "Famine" in Makkah (vv. 75-76), which according to authentic traditions occurred during the middle stage of Prophethood. Moreover, according to a tradition related by 'Urwah bin Zubair, Hadarat Umar who had embraced Islam by that time, said, "This Surah was revealed in my presence and I myself observed the state of the Holy Prophet during its revelation. When the revelation ended , the Holy Prophet remarked, 'On this occasion ten such verses have been sent down to me that the one who measures up to them, will most surely go to Paradise'. Then he recited the initial verses of the surah." (Ahmad, Tirmizi, Nasai, Hakim).
The central theme of the surah is to invite the people to accept and follow the Message of the Holy Prophet and the whole Surah revolves round this theme.
The fact that the people who have accepted the Message of the Holy Prophet have started acquiring such and such noble qualities of character is a practical proof of the truth of the Message. 1 - 11
In this passage, attention has been drawn to the creation of man and the universe to impress that the whole universe including man's own self, is a clear proof of the truth of the Holy Prophet's Message, which invites the people to accept Tauhid and life in the Hereafter. 12 - 22
Then the stories of the former Prophets and their communities have been cited as historical evidences of the truth of the Message. They prove the following things :
The objections and the doubts that the antagonists are raising against the Message of Muhammad (Allah's peace be upon him) are not new. These were raised against the former Prophets also whom they themselves acknowledged as Messengers of Allah. Therefore they should learn a lesson from their history and judge for themselves whether the Prophets were in the right or their objectors.
The Message of Tauhid and the Hereafter that Muhammad (Allah's peace be upon him) is conveying is the same as was brought by the former Prophets; therefore they should accept it.
They should take a warning from the consequences met by those communities who rejected the Message of their Prophets.
All the Prophets brought one and the same religion from Allah and they all belonged to one and the same community. All other religions were invented by the people themselves and none of them is from Allah. 23 - 54
After relating the stories of the Prophets, a fundamental principle has been enunciated: Success and prosperity in the worldly life is not a criterion of success in the sight of Allah. If some persons (or a person) are enjoying prosperity, wealth, power and the like in this world, it does not mean that they are favorites of Allah. Likewise, the poverty and adversity of other people is not a proof that Allah is displeased with them. The real criterion is Faith (or lack of it). This declaration was needed because the antagonists of the Holy Prophet were the great chiefs of Makkah, who (and their followers) were deluded by their own prosperity that God and their deities were well pleased with them. On the other hand, they argued, the fact that Muhammad (Allah's peace be upon him) and his followers were indigent and in a state of helplessness, was a clear proof that Allah was not pleased with them, and they were under the curse of their deities. 55 - 67
In this passage different arguments have been used to convince them that Muhammad (Allah's peace be upon him) was a true Prophet of Allah. Then they have been told that the Famine (vv. 75 - 76) was merely a warning and therefore "it is better for you to mend your ways; otherwise you will be visited by a terrible scourge." 68 - 77
Again they have been invited to observe the Signs in the universe and in their own selves because these are clear proofs of the truth of the Message of the Holy Prophet. 78 - 95
The Holy Prophet has been told not to adopt any wrong way in retaliation to counteract the evil ways of the enemies, and to guard against the incitement of Satan. 96 - 97
In this concluding passage, the enemies of the truth have been warned that they shall have to render an account in the Hereafter and bear the consequences of their persecution of the Believers; therefore they should mend their ways. 98 - 118
Source: Sayyid Abul Ala Maududi - Tafhim al-Qur'an - The Meaning of the Quran