We talk a lot, in the Church, about the Communion of Saints. But there are lots of misconceptions about this doctrine, by Protestants and Catholics alike, I'd like to try to clear some up.
What is it?
The Church teaches that the Body of Christ is one, but even as we are one, we exist in three separate states; the Church Militant (here on earth), the Church Suffering or the Church Penitent (those being purified in purgatory), and the Church Triumphant (those in heaven).
"The three states of the Church. "When the Lord comes in glory, and all his angels with him, death will be no more and all things will be subject to him. But at the present time some of his disciples are pilgrims on earth. Others have died and are being purified, while still others are in glory, contemplating 'in full light, God himself triune and one, exactly as he is"'
These three states exist as one, in a similar way that the three Persons of the Holy Trinity exist in an eternal oneness.
The way that these three states of the Church cooperate and coexist together in the work of Christ and for the salvation of souls is called The Communion of Saints.
How do we partake in this spiritual communion?
How we interact with the saints, and them with us, or even why we interact in the first place is a matter of confusion for Catholics and scandal for Protestants. I'd like to address this over the next few paragraphs.
When we die we are immediately judged, this is called the particular judgment.
CCC 1022 says:
"Each man receives his eternal retribution in his immortal soul at the very moment of his death, in a particular judgment that refers his life to Christ: either entrance into the blessedness of heaven-through a purification or immediately, -- or immediate and everlasting damnation."
Those made righteous by the death and resurrection of Christ go to heaven (some people possibly needing the cleansing of Purgatory, but that's a topic for another day). Those who did not accept the free gift of salvation are condemned, by their own free will and rejection of God's plan, go to hell.
But to call a Christian that has passed on "dead" is kind of a misnomer, because we are not dead but fully alive. As Jesus Himself said, when talking to the Sadducees, " ' I am the God of Abraham, and the God of Isaac, and the God of Jacob'? He is not God of the dead, but of the living." (Matthew 22:32)
We also see this during the Transfiguration, when Jesus is speaking to both Moses and Elijah, "And behold, there appeared to them Moses and Elijah, talking with him." (Matthew 17:3) . Some might say that Elijah never actually died, and they would be correct, but Moses died and had been dead for around 1500 years (Deuteronomy 34). The Transfiguration proves that those who died on earth are still alive, but in a changed state.
We know that the righteous dead are actually alive, and as St. Paul said, "we are surrounded by so great a cloud of witnesses." (Hebrews 12:1) This verse comes immediately after 11 verses, in chapter 11, that spoke of heroes and martyrs for God throughout the history of Israel. These witnesses (the word martyr actually comes from the Greek word meaning "witness") surround us, just as God's Angels surround us, and they are praying for us and cheering us on!
So what does this all mean for us? In John's book of Revelations we see the twenty-four elders (who are definitely human and usually thought to be deceased believers) interceding on our behalf, "And when he had taken the scroll, the four living creatures and the twenty-four elders fell down before the Lamb, each holding a harp, and with golden bowls full of incense, which are the prayers of the saints" (Revelation 5:8) Incense was used, in the temple worship of God, to represent the prayers of His people rising up to Him in heaven. The imagery would be familiar to a Jew (St John's intended audience) around the time of St. John's writing, and serves the same purpose in heaven as it did on earth.
Also we see the martyrs interceding with God on behalf of His persecuted Church, "When he opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the witness they had borne; they cried out with a loud voice, "O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell upon the earth?" (Revelation 6:9-10)
Through the Scriptures we are instructed to pray for each other. St Paul tells us, "Pray at all times in the Spirit, with all prayer and supplication. To that end keep alert with all perseverance, making supplication for all the saints..." (Ephesians 6:18)
Also he says, "First of all, then, I urge that supplications, prayers, intercessions, and thanksgivings be made for all men, for kings and all who are in high positions, that we may lead a quiet and peaceable life, godly and respectful in every way. This is good, and it is acceptable in the sight of God our Savior..." (1 Timothy 2:1-3)
St James tells us, "pray for one another, that you may be healed. The prayer of a righteous man has great power in its effects. (James 5:16b) Not only are we instructed to pray for one another, but we are also told that the prayers of "a righteous man" has great power. Who is more righteous than those in heaven with God? Seems like having them pray for you would be a good idea!
The Angels too are offing our prayers to God for us, "And another angel came and stood at the altar with a golden censer; and he was given much incense to mingle with the prayers of all the saints upon the golden altar before the throne; and the smoke of the incense rose with the prayers of the saints from the hand of the angel before God. (Revelation 8:3-4)
Saints Paul and James' commands to pray for one another does not end at death. Since we are all one body, in three states, it's logical to see why we believe that the Holy Saints of God are, right now, praying for you and me. If they are praying for us then asking them to pray for a specific intention not only makes sense but should be practiced by all Christians.
CCC 956 "The intercession of the saints. "Being more closely united to Christ, those who dwell in heaven fix the whole Church more firmly in holiness. . . . They do not cease to intercede with the Father for us, as they proffer the merits which they acquired on earth through the one mediator between God and men, Christ Jesus . . . . So by their fraternal concern is our weakness greatly helped"