The human soul has sojourned in lower and higher forms, migrating from one to another according to the samskaras or impressions, but it is only in the highest form as a human being that it attains to freedom.
Higher than the question of our duration is the question of our deserving. Immortality will come to such as are fit for it, and he would be a great soul in future must be a great soul now.
Books never make religions, but religions make books. We must not forget that. No book ever created God, but God inspired all the great books. And no book ever created a soul.