When you previously rebelled?
When you previously rebelled?" In other words, "Why did you not repent an hour before when you were quite free to do so?" For, then, it would have been a true change of heart. What criminal in the world is not penitent at the moment of punishment? But if he shows a regret and penitence before he is caught, then we can say he is changing spiritually.
Now, as for why repentance in the next world is unacceptable, this is because the criminal witnesses punishment there and the consequence of his deeds and therefore his repentance would not be a true revolution. Moreover, death is like the fall of a fruit from the tree. As long as it is a part of the tree, it is dependent on the air, water and nourishment that the tree obtains.
Even an hour before falling, there is the chance for that fruit to become more ripe and sweet but the moment it falls every possibility of development comes to an end for it. The human being is the fruit of nature with all the potentials for that person to be good or bad. If we adopt worship and devotion, we are being ripened. If we sin, we are plagued like a rotten fruit. Repentance is one of the ways by which one is nourished when one is alive, not in death or after it.
All the changes and revolution and ups and downs are connected with this world while in the next world, they all come to an end and stop. Another example is a baby in the mother's womb. All its nourishment and health are through the mother but the moment it is born, total dependance comes to an end and, a new order is established for its life that is quite different from the previous one. In the next world, too, everything is different from the order of this world.
Imam Ali (as), peace be upon him, says, 'Today is the time of deeds and not reckoning and tomorrow (in the hereafter) is the time for reckoning and not for deeds.' He does not mean that there is no punishment in this world. Some of the misfortunes which befall us are punishments. But again it does not mean that all punishments for wicked deeds are inflicted in this world. Therefore, if one receives no punishment here it does not mean that one is quite chaste and that one's account is clear.
On the other hand, if a happening like a flood destroys people, is it due to their deeds and their punishment in the world? No. The above saying of Imam Ali (as) says that as this world is for deeds and not for reckoning, the next world is for reckoning and not deeds.