Because the child has forgotten this simple truth, like a child separated from his parents soon after birth, much like the story of Mowgli reared by the animals. Even the child of man grows through the years passing through the animal stages, educates and evolves into a human. The same process applies in the development of the seed of divinity in us. That is why Sri Aurobindo bridges the gap what we are in our essence and what we should be by using the word must. And again since we are his human portion we must ‘grrow’ Divine. And all who sincerely wish to be so have the Help as well as the example of the Avatar.
Affectionately,
Alok Da