All Saints Day

Fra Angelico - 1428-30, Tempera on wood - National Gallery, London

The Church has always honoured those early witnesses to the Christian faith who died as martyrs. During the first three hundred years Christians were persecuted, often suffering torture and bloody death. They refused to deny Christ, even when this denial might have saved their own lives, or the lives of their children and families.

Many of those especially holy people whose names and stories were known, the Church later canonized (that is, the Church formally recognized that the life of that person was without any doubt holy, or sanctified -- a "saint" who is an example for us). The Church's calendar contains many saint's days.

But there were thousands and thousands of early Christian martyrs, the majority of whose names are known only to God -- and throughout the history of the Church there have been countless others who really are saints, who are with God in heaven, even if their names are not on the list of canonized saints.

In order to honour the memory of these unnamed saints, the Church dedicated a special feast day so that all living Christians would celebrate at a special Mass the lives and witness of those "who have died and gone before us into the presence of the Lord".

All Saint's Day, originated as a feast of All Martyrs, sometime in the 4th century. At first it was celebrated on the first Sunday after Pentecost. It came to be observed on May 13 when Pope St. Boniface IV (608-615) restored and rebuilt for use as a Christian church an ancient Roman temple which pagan Rome had dedicated to "all gods", the Pantheon. The pope re-buried the bones of many martyrs there, and dedicated this Church to the Mother of God and all the Holy Martyrs on May 13, 610.

About a hundred years later, Pope Gregory III (731-741) consecrated a new chapel in the basilica of St. Peter to all saints (not just to the martyrs) on November 1, and he fixed the anniversary of this dedication as the date of the feast.

A century after that, Pope Gregory IV (827-844) extended the celebration of All Saints to November 1 for the entire Church.

The vigil of this important feast, All Saint's Eve, Hallowe'en, was apparently observed as early as the feast itself.

Ever since then, the entire Church has celebrated the feast of All Saints on November 1st, and Hallowe'en on October 31.

Wikiipedia, All Saints for more information