The Creed and core doctrine · Question 10
Does ‘the communion of saints’ mean secretly communicating with dead people?

The question: “How is asking a saint for help any different from calling up a spirit?”
The Church's answer: ‘The communion of saints’ means the fellowship of the Church, which forms one body in Christ through the Holy Spirit. ‘Saints’ here is not only the few who have been canonized but everyone who belongs to Christ, and ‘communion’ means sharing together in holy things and in the gifts of love. Believers on earth, those being purified, and the saints in heaven are not completely cut off from the one body of Christ by death.
So the Church prays for the dead, and asks the saints in heaven to pray to God for us. That is a different thing from summoning a spirit to get hidden information or to tell the future. The saints do not stand in for God, nor do they take away the one mediation of Jesus Christ. Every help and every prayer happens through Christ, inside the one body.
An analogy — one family praying for each other
Asking a friend “please pray for me” is not abandoning Jesus. The intercession of the saints resembles that, in that it is a fellowship of praying for one another in Christ. But the life of the Church in heaven cannot be drawn exactly like a family on earth, and this analogy doesn't mean it is fine to call up the dead for a conversation or for information.
If they press further: “Then do we worship the saints the way we worship God?” — no. Adoration is given to the Triune God alone. With the saints we rejoice at the fruit God's grace has borne in a human life, we honor them, and we ask them to pray for us.
In one sentence: “‘The communion of saints’ isn't calling up spirits; it's the fellowship in which the living and the dead form one body in Christ and share holy things and prayer.”