Reincarnation is a wonderful demonstration of God's grace and our ability to correct that which needs to be corrected. It seems inconceivable that we can master the lower aspects of the personality in one earthly lifetime. Reincarnation helps explain the appearance of evil in a world guided by a loving God. Seasons come and go. People are born and die.
Trees follow a cyclic pattern of life and apparent death.
History seems to repeat itself, until there is no longer a need to repeat the cycle. The cycle of rebirth is one of many cycles in which we are involved. That would be a cruel and mindless God. Through reincarnation, we are given the opportunity to set straight that which may have gone wrong. Through reincarnation, we are given the opportunity to come back with another spirit, or group of spirits, to make good that which may be bad, or to make even better that which is already good.