The sura takes its name Al-Muminun from the first verse.
Period of Revelation
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 sura 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 Sura 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 sura. (Ahmad Tirmizi Nasai Hakim).
The central theme of the sura is to invite the people to accept and follow the Message of the Holy Prophet and the whole Sura revolves round this theme.