Alarming the Idolators with News of the Day when the Sky will bring forth a visible Smoke

Allah says, these idolaters are playing about in doubt, i.e., the certain truth has come to them, but they doubt it and do not believe in it. Then Allah says, warning and threatening them:

فَارْتَقِبْ يَوْمَ تَأْتِى السَّمَآءُ بِدُخَانٍ مُّبِينٍ

لَيْلَةٍ مُّبَارَ‌كَةٍ 'blessed night', in verse 2 according to majority of the Commentators, refers to 'laylatul Qadr' or the 'Night of Power' which occurs in the last ten nights of the month of Ramadan. During this night Allah sends down countless blessings for his slaves/servants. It has been explicitly mentioned in Surah Al-Qadr, thus:

إِنَّا أَنزَلْنَاهُ فِي لَيْلَةِ الْقَدْرِ‌