Overall meaning : As for those who disbelieve in their Lord and deny His Messengers, their good deeds which they have done thinking they would benefit them will in fact go unrewarded: They are like a mirage in an open space with no buildings, trees or plants. The thirsty traveller thinks it is water, but when he comes near he finds that it is nothing. Such is the case of the unbelievers who think their good deeds will benefit them. They will realise, after their resurrection from death, that such deeds have gone unrewarded. Instead, they will find their Lord there to pay them their account in full. Allah is swift in taking account of people’s actions.
Or their actions are like darkness in a deep sea, covered by waves above which are waves, above which are dark clouds: layers of darkness, one above the other. If whoever is engulfed in such darkness stretches out his hand, he will by no means see it due to the intensity of the darkness. Those Allah does not guide to faith and does not illuminate their heart with the light of Islam will find no one to guide them at all.