Four, beauty of stability
All numbers have a personality and the four’s personality is of balance, stability and knowledge. We use it to build our structures, to layout a coordinate system and to even navigate our way across the earth with our cardinal directions (N,S,E,W). Perpendicular and parallel lines are inherent to the square and even show up when writing the number four. Perpendicular and parallel lines are how we come to know things in the material world and this is why the square is symbolic for knowledge.