The Spring Equinox is the date upon which the liturgical calendar of the Church is based. All of the moveable Feasts of the Church depend on Easter, which falls on the first Sunday after the first full moon after the Spring Equinox.
On the day of an equinox, day and night are of approximately equal duration. After the equinox, day becomes longer than night (i.e. Light overpowers darkness). Therefore the Spring Equinox symbolizes the appearance of Light and the awakening of nature.
The full moon marks the opposition of the Sun and Moon, astronomically. In the ancient traditions, the Planetary Genius of the Sun is Mikael, who became the Christian Saint Michael. The opposition of the Night Star to the Day Star is, exoterically, the battle of Mikael and Lucifer, Typhon-Set and Osiris, Ormuzd and Ahriman.
Easter commemorates the victory of Mikael on the first day governed by the Sun (Sunday), after the mythical battle…
(Adapted from “In the Shadow of the Cathedrals” by Robert Ambelain, Trans. P. Vaughn.)
“In the afternoon of the spring equinox, weigh and measure your prima material. Purify it, separate the elements, and then aid and promote the action of Nature. Consecrate the generating crucible, awaken the god hidden in matter, with prudence and according to the traditional rites and age-old experience. Free the mineral spirit enclosed in your prima material, wash and purify it, vivify it using the Fire Principle, and for that still follow Mother Nature.”
- Pseudo-dedication of Jehan de Chelles to the Virgin Mary.
(Source: Ambelain, Robert. "In the Shadow of the Cathedrals.")