All Saints' Day is also commemorated by members of the Eastern Orthodox Church as well as some protestant churches, such as Lutheran and Anglican churches.Generally, All Saints' Day is a Catholic Holy Day of Obligation, meaning all Catholics are required to attend Mass on that day, unless they have an excellent excuse, such as serious illness.
Other Christian traditions define, remember and respond to the saints in different ways.
The feast of All Saints achieved great prominence in the ninth century, in the reign of the Byzantine Emperor, Leo VI "the Wise" (886.911).
In the Roman Catholic Church, the next day, All Souls' Day, specifically commemorates the departed faithful who have not yet been purified and reached heaven.
Catholics celebrate All Saints' Day and All Souls' Day in the fundamental belief that there is a prayerful spiritual communion between those in the state of grace who have died and are either being purified in purgatory or are in heaven (the 'church penitent' and the 'church triumphant', respectively), and the 'church militant' who are the living.
All Saints' Day was formally started by Pope Boniface IV, who consecrated the Pantheon at Rome to the Virgin Mary and all the Martyrs on May 13 in 609 AD.