During the course of a year, the sun passes through four cardinal points: the vernal equinox on 21 March; the summer solstice on 21 June; the autumn equinox on 21 September; the winter solstice on 21 December. These are four moments in nature when there are large influxes of energies affecting all forms of life.
On the wheel of the Zodiac, spring begins with Aries, a fire sign; summer begins with Cancer, a water sign; autumn with Libra, an air sign; and winter with an earth sign, Capricorn.
Therefore, the start of each season is linked with one of the four elements.
Each element is governed by powerful entities who command myriads of servants responsible for spreading the new currents of energy accross the surface of the planet. The universe is not a machine, and the movements that drive it are not set off mechanically: each change is produced by the work of living beings invisible to us, with the responsibility of taking particular care of stones, plants, animals, or humans.