One of the most underappreciated teachings of the Church is her understanding of the communion of saints. Just as the Church is called to be “holy” or “set apart,” so too, the saints are “holy ones,” those set apart from the world. Baptism inserts us into the communion of the Church and thereby places the call upon us to be saints. This communion, though, doesn’t simply hold to those here on earth. It extends to those in the Church suffering, in purgatory, as well as those in the Church triumphant, in heaven. The communion of saints is made of all Christians who are members of the one body of Christ.
This implies that the Church here on earth is called to be in communion with one another. This communion is guaranteed and strengthened by our reception of Holy Communion where Jesus gives us his body to be more fully his body, the Church. Thus, when we sin seriously, when we do not hold on to what Christ has given us in faith, we refrain from receiving Communion because we are saying: through my actions and beliefs, I am not in communion with Christ and his Church.
This communion, though, is a real bond between the three “states” of the Church. Those who have gone before us are not separated from us. They are, in fact, more alive than we here on earth. Hence, in Preface I for the Funeral Mass we exclaim: “indeed for your faithful, Lord, life is changed, not ended.” The communion of saints implies that death is not the last word, and that there is a real bond between those on earth, those in purgatory, and those in heaven.