It is useless to object that forgetfulness constitutes a barrier against the utilization of experience acquired in past lives. If God considered it convenient that a veil be cast over the past it is because it is to our advantage that this be so. In fact, remembrance would be a very great inconvenience. It could in certain cases, cause a person great humility or perhaps make them prideful, which would interfere with their free will. In any case it would certainly cause inevitable perturbation in social relationships.
A Spirit is frequently reborn into the same ambient where it has previously lived, establishing once again the same relationships, in order to repay the evil done. Recognition of these same persons, who perhaps had been hated, would only serve to rekindle that emotion. In any case, humiliation would be felt on confronting those who had been offended. So in order that we may improve ourselves God has bestowed upon us precisely what we need, that which is sufficient and nothing more, this being none other than the voice of conscience and our instinctive tendencies. He has only deprived us of what would be prejudicial.
On being reborn, Man brings with him what he has acquired. He is born exactly the way he has made himself. In each life he begins from a new starting point. It matters little to him to know what he was before. If he finds himself being punished it is because he did wrong. His actual tendencies indicate what is still to be corrected, and it is upon this he should concentrate all his attention, seeing that no trace is left of what has been rectified. The good resolutions he feels bound to make are the voice of conscience, calling attention to what is right and what is wrong, so giving strength to resist temptation.
Moreover, this forgetfulness only occurs during bodily existence. On returning to the spiritual world the remembrance of the past is regained. So it is only temporary, a slight interruption similar to that which occurs during sleep, but which does not prevent the remembrance on the subsequent day of what was done on the previous one.
But it is not only after so-called death that the Spirit may recover remembrance of the past It can be said that it is never lost, even whilst incarnate, as experience demonstrates that during sleep, being a period when a certain amount of liberty is enjoyed, the Spirit is conscious of its past acts. It knows why it is suffering and that it suffers justly. Memory is only extinguished during the course of exterior existence, in the life of relationships. But during these partial remembrances, which if they were otherwise might cause added suffering and harm social relations, the Spirit absorbs new strength in these moments of emancipation of the soul, if it knows how to take advantage of them.
Gospel according to Spiritism. Chapter V, item 11