What is "communion of saints"

The communion of saints (in Latin, communio sanctorum), when referred to persons, is the spiritual union of the members of the Christian Church, living and the dead, those on earth, in heaven, and, for those who believe in purgatory, those also who are in that state of purification. They are all part of a single " mystical body", with Christ as the head, in which each member contributes to the good of all and shares in the welfare of all.

The earliest known use of this term to refer to the belief in a mystical bond uniting both the living and the dead in a confirmed hope and love is by Saint Nicetas of Remesiana (ca. 335–414); the term has since then played a central role in formulations of the Christian creed. Belief in the communion of saints is affirmed in the Apostles' Creed.

The word "sanctorum" in the phrase "communio sanctorum" can also be understood as referring not to holy persons, but to holy things, namely the blessings that the holy persons share with each other, including their faith, the sacraments and the other spiritual graces and gifts they have as Christians.