Musar zu Ijow 1:7

The second aspect of one's lifestyle which will be subject to examination is the use one has made of one's mouth concerning the food one ate. Did one consume food with the intention of increasing one's sanctity? The Torah describes winged creatures which primarily use their legs to move with (11,21). There appears to be a symbolism here. Does one ignore one's wings, symbol of flying to higher regions, in favor of לנתר על הארץ, jumping around merely on earth, thus signalling one's preference for the physical aspects of this universe? Permission to eat the species which לא כרעים, do not use their feet in preference to their wings but rather strive towards the spiritual regions לו, symbolizes why one should eat and what motivation should guide one when eating.