Allah mentions the condition of the disbelievers when they are made to stand before the Fire on the Day of Resurrection and witness its chains and restraints, along with seeing the horrible, momentous conditions in the Fire with their own eyes. This is when the disbelievers will say,
("Would that we were but sent back (to the world)! Then we would not deny the Ayat of our Lord, and we would be of the believers!") They wish that they would be sent back to the life of the world so that they could perform righteous deeds, refrain from disbelieving in the Ayat of their Lord and be among the believers. Allah said,
(Nay, what they had been concealing before has become manifest to them.) meaning, the disbelief, denial and rebellion that they used to hide in their hearts will then be uncovered, even though they will try to hide this fact in this life and the Hereafter. Earlier, Allah said,
(There will then be (left) no trial for them but to say: "By Allah, our Lord, we were not those who joined others in worship with Allah." Look! How they lie against themselves! But the (lie) which they invented will disappear from them. ) It is also possible that the meaning here is that the disbelievers will realize the truth that they knew all along in their hearts, that is, that what the Messengers brought them in this life is true, although they used to deny his Message before their followers. Allah said that Musa said to Fir`awn,
("Verily, you know that these signs have clearly been sent down by none but the Lord of the heavens and the earth as eye-opening evidence.") 17:102 Allah said about Fir`awn and his people,
(And they belied them (those Ayat) wrongfully and arrogantly, though they were themselves convinced thereof.) 27:14
(Nay, it has become manifest to them what they had been concealing before.) 6:28 When this occurs, and the disbelievers ask to be returned to this life, they will not do so because they truly wish to embrace the faith. Rather, they ask to be returned to this life for fear of the torment that they are witnessing before them, as punishment for the disbelief they committed, and to try and avoid the Fire that they see before their eyes.
(But if they were returned, they would certainly revert to that which they were forbidden. And indeed they are liars.) meaning, they lie when they say they wish to go back to this life so that they can embrace the faith. Allah states that even if they were sent back to the life of this world, they will again commit the disbelief and defiance that they were prohibited.
(And indeed they are liars.) in their statement that,
("Would that we were but sent back! Then we would not deny the Ayat of our Lord, and we would be of the believers!" Nay, what they had been concealing before has become manifest to them. But if they were returned, they would certainly revert to that which they were forbidden. And indeed they are liars. And they said: "There is no (other life) but our (present) life of this world, and never shall we be resurrected.") Therefore, they will revert to their old behavior and say,
(There is no life but our life of this world) and there is no Hereafter,
(and never shall we be resurrected. ) Allah said,
(If you could but see when they will stand before their Lord!) in front of Him,
("Is not this the truth") meaning, is not Resurrection true, contarary to what you thought,
(They will say: "Yes, by our Lord!" He will then say: "So taste you the torment because you used not to believe.") and because you today denied Resurrection. Therefore, taste the torment,
("Is this magic, or do you not see") 52:15