Wherefore come out from among them, and be ye separate,
saith the Lord, and touch not the unclean thing;
2 Corinthians 6:17
"The feast of All Saints has a long history in the Church and at one point enjoyed the pride of place of Octave, which is only reserved for Christmas and Easter these days. As Fr. Grunow points out over at Word on Fire, the feast began in earnest in the 7th Century:
The practice of a festival day to honor the whole communion of Saints, rather than that just a single saint, seems to happen for the first time in the Catholic Church with the consecration of the Pantheon as a public place for the Church’s worship. This happened in
the year 609 (or 610) on May 13th. The Pantheon had been originally dedicated for the use of Roman religion as a place where all the gods would be honored. Boniface displaced the images of the gods from their shrines and gave the building over to the Saints of the Church, particularly the Martyrs. This was a kind of “in your face” to pagan culture. Boniface was saying that the old gods had been defeated and were defeated by the faith of the Church’s Martyrs… How we get from May 13th to November 1st is interesting. The festival of All Saints seems to emerge from the dedication of another Roman church that was consecrated by Pope Gregory III. The church is named St. Peter and all the Saints. It was a subsequent pope, Gregory IV, who extended the annual festival that commemorates this church dedication to the whole Church as All Saints Day. The extension of festivals specific to the Church of Rome is part and parcel of how the Catholic Faith becomes the underlying cultural matrix from which a new kind of European civilization would emerge." CatholicExchange
