When an unbaked pot is broken, the potter can use the mud to make a new one; but when a baked one is broken, he cannot do the same any longer. So when a person dies in a state of ignorance, he is born again but when he becomes well baked in the fire of true knowledge and dies a perfect man, he is not born again.
A grain of boiled paddy does not sprout again when sown. Only unboiled paddy sends forth the shoot. Similarly when one dies after becoming a Siddha, a perfect man, he has not to be born again, but an Asiddha, an imperfect man, has to be born again until he becomes a Siddha.
........SRI RAMAKRISHNA