What kind of mental state does the meditation on four elements generate? In the Maha-satipatthana Sutta (DN22), the mindfulness about the elements is taught:


  “There are in this body, the earth element, the water element, the
  fire element, the wind element.”
  
  Just as though, monks, a clever butcher, or a butcher’s apprentice,
  after slaughtering a cow, were sitting down at a crossroads after
  dividing it into portions; even so, monks, a monk in regard to this
  very body, however placed, however disposed, reflects by way of the
  elements:
  “There are in this body, the earth element, the water element, the
  fire element, the wind element.”


However I am unable to understand why we have to look at the elements from the clever butcher's point of view. What kind of mental state does the meditation on elements generate? Please explain the analogy in detail.
I don't know but maybe this passage about a skilled butcher from chapter III of the Book of Zhuang Zi is a clue.


  Prince Hui's cook was cutting up a bullock. Every blow of his hand,
  every heave of his shoulders, every tread of his foot, every thrust of
  his knee, every whshh of rent flesh, every chhk of the chopper, was in
  perfect harmony,—rhythmical like the dance of the Mulberry Grove,
  simultaneous like the chords of the Ching Shou.
  
  "Well done!" cried the Prince. "Yours is skill indeed."
  
  "Sire," replied the cook; "I have always devoted myself to Tao. It is
  better than skill. When I first began to cut up bullocks, I saw before
  me simply whole bullocks. After three years' practice, I saw no more
  whole animals.
  
  And now I work with my mind and not with my eye. When my senses bid me
  stop, but my mind urges me on, I fall back upon eternal principles. I
  follow such openings or cavities as there may be, according to the
  natural constitution of the animal. I do not attempt to cut through
  joints: still less through large bones.
  
  "A good cook changes his chopper once a year,—because he cuts. An
  ordinary cook, once a month,—because he hacks. But I have had this
  chopper nineteen years, and although I have cut up many thousand
  bullocks, its edge is as if fresh from the whetstone. For at the
  joints there are always interstices, and the edge of a chopper being
  without thickness, it remains only to insert that which is without
  thickness into such an interstice.
  
  By these means the interstice will be enlarged, and the blade will
  find plenty of room. It is thus that I have kept my chopper for
  nineteen years as though fresh from the whetstone.
  
  "Nevertheless, when I come upon a hard part where the blade meets with
  a difficulty, I am all caution. I fix my eye on it. I stay my hand,
  and gently apply my blade, until with a hwah the part yields like
  earth crumbling to the ground. Then I take out my chopper, and stand
  up, and look around, and pause, until with an air of triumph I wipe my
  chopper and put it carefully away."
  
  "Bravo!" cried the Prince. "From the words of this cook I have learnt
  how to take care of my life."


Since the elements are really expressing states i.e. water is not really water but liquid, wetness, changing, the idea is perhaps about the composition (and decomposition) of bodies. Individual bodies like yours and mine but also the larger structures we belong to: our families, our nations, the international community etc., which also function like bodies, where different people playing different roles and where mind work is at the top and support work is at the base. In starvation, the human body will take food from itself to feed the brain and keep it going and will only take from parts of the brain to feed the most important parts of the brain when it has no choice. And what is an ox/bullock in the ancient world? The source of work/energy. Hence harnessing/yoking and the plough.