It is according to the aspiration and according to the necessity. You may have the aspiration to do something, but at the same time God may not feel the necessity for you to do it. From your side aspiration is necessary. You are aspiring to come back again and to start the game again immediately. It is as if you have played for half an hour and now you are taking a short rest. Then, if you do not want to rest any longer, you say: “Give me the opportunity to finish the game and go back.” But God may say, “No, I want you to take rest for a while longer.” At that time you cannot return. But if your aspiration and God’s necessity become one, then certainly you can come back.
Some souls reincarnate almost immediately, without even going to the soul’s region. Suppose somebody dies prematurely in an accident. At that time his soul may go only up to the vital sheath and from there, if a spiritual figure or the Divine Grace intervenes, in seven or eight months it will take incarnation in a new family.
Most ordinary souls come back again after staying in the soul’s world for six or seven or, at most, twenty years. The time in the soul’s world is used by the soul to assimilate its experiences on earth. Great people, such as great scientists or spiritual figures, do not take birth again as rapidly as ordinary people. Very rarely will you see a great figure in any field who will take incarnation again very soon. Some stay in the soul’s world for seventy years or more. In certain cases, spiritual Masters wait a hundred or two hundred years before reincarnating. But there is no hard and fast rule. If the Supreme wants them to come back to earth, they have to come back even if they do not want to. It is the soul’s own decision, plus the approval of the Supreme, that determines how long it takes for a person to reincarnate.
by Sri Chinmoy