Four is the number of order, structure and the material world, and its symbolism is unusually consistent across traditions because it rests on things that are actually fourfold: the four directions, the four winds, the four seasons, the four classical elements, the four rivers of paradise, the four corners of the earth. Four points make the first solid figure in three dimensions, the tetrahedron, and four is the first composite number and the first square after one, two times two, the number that encloses area and builds foundations. From this comes its steady association with the earth, the body, stability, the square and the four-square reliability of what is fixed and grounded.
In modern numerology four is the number of work, order, discipline, foundation and the builder, solidity and patient labour, sometimes read as rigidity. That character belongs to the early-twentieth-century American numerology, not to antiquity; what is genuinely ancient is the association of four with the material and the ordered, which rests on the fourfold divisions of the world rather than on any doctrine of the digit.