Sri Aurobindo is able to construct this dichotomy as the essence of the relationship between the human being and the divine.  The basic idea that is taken from this quote comes from a poem that Sri Aurobindo wrote on the basic idea of how he sees a tree.  The critical element is that the tree is rooted in the ground, and yet strives for the sky.  In this, there is what Aurobindo identifies as the intrinsic condition of what humanity is.  On one hand, the condition of man is one where there is division between he and the divine.  The notion of "heavenly flight" is inhibited by our own humanity.  The soul becomes the embodiment of how painful this condition can be, one that Sri Aurobindo identifies as the essential predicament for humanity.  The idea of being "hungry for Earth" is one where detachment is impossible because of want and ego, conditions that define what our condition as being "human" is all about.  This "hunger" for that which is temporal and contingent is what detains our hope for transcendence, what Sri Aurobindo would identify as "our heavenly flight."  I don't see that Sri Aurobindo is identifying this as a painful condition or one that makes humanity agonizing.  Rather, in referencing the tree as the subject of his poem, Sri Aurobindo is suggesting that we as human beings identify this as a condition of our being in the world, embracing that which might be impossible to overcome and simply accept it as fact.  In this, there is a tacit understanding that our functions as human beings might not never be fully complete and this is understandable for we surrender our own sense of ego and notion of self, indicating submissiveness to something beyond ourselves and not detaining for so long our "heavenly flight."