Zacharias 8:19 records the tradition of fasting four times a year to focus on God through His creation:
Thus saith the Lord of hosts: The fast of the fourth month, and the fast of the fifth, and the fast of the seventh, and the fast of the tenth shall be to the house of Juda, joy, and gladness, and great solemnities: only love ye truth and peace.
The Catholic seasonal fasts are called Ember days (the word comes from the old Anglo-Saxon ymbren, a circuit or revolution), and they coincide roughly with the change of the seasons: the week between the third and fourth Sundays of Advent (Winter), between the first and second Sundays of Lent (Spring), between Pentecost and Trinity Sunday (Summer), and the week beginning on the Sunday after Exaltation of the Holy Cross (September 14 — Autumn). The days were inconsistent until Pope Innocent II fixed them at the Council of Clermont in 1095.
We fast and abstain on the Wednesday, Friday, and Saturday of each Ember week.
The solemn fast of the three days in Ember Week, originally peculiar to the Roman Church, was afterwards borrowed by the other Latin dioceses. Pope St. Leo I explained the Ember Days saying that at the end of the year it is especially fitting that we dedicate the first fruits to the Divine Providence.
An ancient tradition reserved the ordinations of priests and deacons to the month of December, and the faithful, following a custom introduced by the Apostles themselves, felt constrained to unite with the bishop in prayer and fasting, in order to call down from God an abundance of priestly gifts upon the heads of those newly chosen to minister at the altar.
Formerly, after assembling, the procession of clergy and people, chanting the Litany, went from St. Peter in Vinculis to St. Mary Major by way of the Suburra, between the Viminal and the Esquiline hills. Today’s station — following the custom for Ember Wednesdays — is at St. Mary Major, in order that the new Levites may be placed under the heavenly patronage of her whom the Fathers of the Church sometimes call the “virgin-priest,” in whose temple the Incarnate Word Himself was anointed priest by the divine Paraclete.