As an extension of the feast of All Saints, the Church used to honor all the relics a specific church possessed.
The Catholic Encyclopedia explains the origin of this separate feast that was popular in the 19th century and early 20th century: “It has long been customary especially in churches that possessed large collections of relics, to keep one general feast in commemoration of all the saints whose memorials are there preserved. An Office and Mass for this purpose [were] found in the Roman Missal and Breviary.”
Dom Prosper Guéranger also recalls this tradition in his Liturgical Year:
As the feast of the Holy Relics is in many places celebrated on the Sunday within the Octave of All Saints we here give the Mass and Vespers most commonly used…Whatever may become of the just under trial and persecution, their bones shall be gathered together again on the last day at the voice of the Son of Man.
This feast is no longer celebrated by the universal Church, though local churches may still observe the concept behind this feast by exposing for veneration the relics in their collection on All Saints Day.
What are relics?
Relics are material items that are connected to a saint and are sorted into three “classes.” A first-class relic is all or part of the physical remains of a saint. This could be a piece of bone, a vial of blood, a lock of hair, or even a skull or incorrupt body.
A second-class relic is any item that the saint frequently used (clothing, for example). A third-class relic is any item that touches a first or second-class relic.
Catholics are known to preserve relics of saints, and it is believed that graces from God flow through these objects to devout souls who venerate them.
Relics of saints allow us to draw close to these holy men and women of the past and God uses these material objects to impart special graces to faithful souls.
They are never to be worshiped, and are meant to lead us to the ultimate worship of the one God.
And today we celebrate...