The theory of evolution is inextricably bound up with the theory of reincarnation. Self-purification which leads to the instantaneous, spontaneous and indescribable realisation of the ever-present self-luminous self, is not possible in a single life-span, though this need not necessarily involve taking birth after birth. You are trapped in this world in which you experience a succession of happiness and unhappiness, success and failure, pleasure and pain. Something is born in you, something dies in you. That itself is enough reincarnation. Each day you are born and you die a thousand times. Every hope is a new birth. Every frustration is a death. With faith you will recognize naturally, in and through these changes, something that is immutable. This is the key to self-realisation.
Even the ‘intervals’ of physical ‘death’ – which is only an unusually extended form of deep sleep – are an indispensable step in this delicate process of purification, meant to ensure that the overall effect of the accomplishments of each life-span is preserved and the cumbersome and distracting details are washed away. Thus, life span after life span, the individual soul is dyed deeper and deeper into the color of God. That is what Jesus meant when he said: Be ye therefore perfect, even as your Father in heaven is perfect. The perfection alluded to here is a perfection equal to the perfection of God.
Krishna specifically mentions that the soul incarnates in worlds other than this; several recent incidents prove that it is possible for the soul to return to this very earth. Even the ‘recall’ of Lazarus by Jesus points to this possibility. However, that we assume a body suitable for further evolution towards divine perfection is certain.
Rightly understood, this doctrine will not cause despair or pessimism because of the length of time this process of self-purification needs. Time itself is relative and illusory: he who vigilantly strives to discover perfection lives in the eternal now.