The saints are venerated on their feastdays.
The first commandment of the Church is the solemn observance of Sundays and holydays.
The early Christians kept a great number of festivals in order to keep alive the memory of certain events or people or benefits received from God as their anniversaries came around; and to thank God for them. Not all feast days are holydays of obligation and these vary from place to place. It is obligatory to keep a holyday of obligation in the same manner as Sundays; we must abstain from servile work and assist at Holy Mass. In cases where it is not possible to attend Mass, for a serious reason such as being obliged to work or through sickness, another form of prayer lasting half an hour should be undertaken instead. Marking the occasion in this appropriate manner is more important than marking it via celebratory meals; which of course are also an important aspect of the celebration of a saint’s feastday.
The seven feasts of Our Lord are Christmas (December 25th), the Circumcision (January 1st), The Epiphany (January 6th); Easter (kept on the first Sunday following the first full moon after the Spring equinox); The Ascension of Our Lord into Heaven (forty days after Easter); Pentecost (fifty days after Easter); and Corpus Christi (the Thursday of the second week after Whitsunday). The Resurrection and the Nativity of Our Lord are the feasts of primary importance and they are celebrated with particular solemnity. All except the Circumcision and Corpus Christi are holydays of obligation in Ireland.
The five feasts of the Mother of God are The Immaculate Conception (December 8th); The Nativity of Our Lady (September 8th); The Annunciation (March 25th); The Purification (February 2nd); the Assumption (August 15th). Of these; the Immaculate Conception and the Assumption are the only ones which are holydays of obligation. Unlike that of other saints, the principal events of the life of Our Blessed Mother are commemorated as it was so intimately connected with the life of the son of God. Unlike the other saints where their birth day in Heaven or their birth to a better life is commemorated; Our Lady’s conception day and her birthday are celebrated because she was conceived and born without sin.
In Ireland, the Feast of All Saints (November 1st) and the Feast of St. Patrick (March 17th) are holydays of obligation.
There are many other feast days which are classed ass ‘first class feastdays’; though they are not holydays of obligation. On these days; it is strongly encouraged to attend holy Mass and to mark the feastday, though doing so is not obligatory.
The choice of feastdays in the past was for various reasons. In some instances; the Church chose feastdays which were sacred to the pagan nations converting to Christianity; to make their transition from paganism easier. For example; the birth of Our Lord is commemorated in the season in which the pagans in the long winter nights in the depths of Winter used to the worship of the sun; in some instances the Church’s festivals were instituted as replacements for the feasts of the Old Testament, which were a foreshadowing of the Christian festivals. For example; in many languages, the name given to Easter comes from a Hebrew word ‘Pasch’ or ‘Passover’ which means Passage through the Red Sea (‘Pascha’ in Latin, ‘Paques’ in French; ‘Pasq’ in Welch; ‘Pasen’ in Dutch or Flemish). Even the theme of the Passover and the theme of Easter (passing from death and slavery in Egypt to life in the Promised Land; and; Christ; by dying on Good Friday and by rising to life on Easter Sunday conquered
death and freed men who become and are one with God from the slavery to sin and death). In English however, the word ‘Easter’ is derived from ‘Eostre’, the name of a pagan Saxon goddess; a Spring festival in her honour was Christianised so that the word became the English equivalent of the Pasch.