The Holy Zohar teaches that a human being lives in an existence of circles and squares.
The square signifies the reality of regimen and law.  A person must behave according to order and within guidelines.  Above the square, though, is the concept of the circle, the circle refers to the concept of faith and superior guidance.  The circle and the square also correspond to the female and male nature of existence.  The essence of life is always finding harmony between these two natures of reality.  
The strings which protrude from the main in the center signify that a human baing through his deeds and words influence the entirety of the the world.