We become different in substance itself. There is a transfiguration of personality. We grow in every sense of the term. It is not like the growth of a baby into an adult, but like the growth of the plant into the animal, the animal into man, and so on, where there is a qualitative increase of knowledge and power. When the child becomes an adult, there is not much of a qualitative change in the species and the way of thinking of the individual.
Man is man.
He does not change. The human way of thinking does not alter merely because we have grown from childhood to the adult stage. But when one grows from the animal to man, there is a change of perspective and understanding and the way of thinking itself. The attitude to life changes. The practice of Yoga is an evolutionary process and not merely a physical growth or a quantitative expansion.