In tarot, we often see the numbers as representing specific energy. As we mentioned in the Emperor, fours represent stability, or taken to a negative extreme, stagnation. Each of the suits in tarot also represents a specific energy. The Wands and Swords are active energy while the Cups and Pentacles are passive energy. It is interesting to see how the energy of the four merges with the energy of the suits to create either a restful or lethargic feeling.
In the active suits, Wands and Swords, the fours show a quiet calmness, with the Swords being peaceful and the Wands being happy or celebratory but not wild (the 3 of Cups has a more wild energy). In both cards there is a nice balance of active and passive, creating a pleasant experience.
In the passive suits, the feeling of the cards is more stagnated. The Cups oozes ennui and boredom. The hoarding taking place in the Pentacles card has a constipated feel. In these two cards, we are mixing too passive energies and the result is sluggish.
All images from the Legacy of the Divine Tarot by Ciro Marchetti