Overall meaning : Remind them, Muhammad, of the time when We raised Mount Sinai high above the Israelites as though it were a cloud shading them, and they were certain it was going to fall on them. We said: Hold fast to the Torah and strictly observe the commandments in it so that you may fear Allah and obey Him.
And mention to the people, Muhammad, the time when your Lord brought forth from the loins of the Children of Adam all their descendants and made them testify against themselves. 'Am I not your Lord?’ He asked. 'Yes,’ they replied, 'We testify that indeed You are.’ He made them testify against themselves lest they should deny this on the Day of Judgement and say, 'We do not know that Allah is alone worthy of worship’; or lest they say, 'Our forefathers associated others with You before our time, and we are merely descendants coming after them and we followed in their footsteps. So are You going to punish us for the doings of our forefathers who invented falsehood instead of worshipping You alone?’
The Almighty then states that just as He has clearly made such verses abundantly clear, so He makes the other verses of the Qur’an perfectly plain so that people may be guided by them.