There are basically two reasons:
- Because they want to.
- Because someone else wants them to and they're unwilling/unable to fight it.
Roman Catholic AnswerHoly Week, the week preceding Easter, starts with Palm Sunday and is the holiest week of the year. During this week the Church commemorates the Passion of Christ, and all the ceremonies reflect this attitude of sorrow, yet joined with gratitude for God's mercy in becoming man in order to suffer and die for a sinful mankind. (from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980). Holy Week begins with the Palm Sunday Mass in which the Passion is read in its entirety and the people hold palms. Later in the week, the Bishop celebrates the Chrism Mass at which he blesses and consecrates the three Oils that will be used by all the priests in his diocese for the coming year. Representatives from each parish bring the oils back to their parish. This Mass is usually celebrated with all the priests of the diocese. On Holy Thursday, the anniversary of the Last Supper, when Christ instituted the Eucharist, the Sacrifice of the Mass, and the sacrament of the priesthood (traditionally the Chrism Mass was on the morning of Holy Thursday). On Good Friday, the only day of the year when Mass is not celebrated, Christ's death on the cross is recalled, Communion is given from reserved Hosts from Holy Thursday, and the Cross is venerated. Holy Saturday ends with the Easter Vigil, the closest Mass we have to one of the Masses of the first century.
