Communion in sacris refers to that which is sacred, usually the sacraments. For example, we have full communion with the Orthodox when it comes to sacraments. They are the same sacraments, equally valid and equally licit.
On the other hand, we are not to receive Holy Communion at an Orthodox Divine Liturgy nor are they to receive Holy Communion at a Catholic mass unless expressed permission is given by the proper authority. It must be understood that the Orthodox are not Protestants either.
With the Protestants, the only sacrament that we have in common is Baptism. Because they do not have validly ordained priests, they cannot validly celebrate any of the other sacraments. We don’t as close a communion on matters that are sacred as we do with the Orthodox. However, we do have communion in other areas such as Sacred Scripture, our faith in Jesus Christ and many of our moral laws.
As to praying with Protestants, it’s never a sin to pray with anyone. Prayer is prayer. If the other person is a pagan, you can certainly pray alongside them, but not engage in their prayers or rituals. It’s a little different with Jews and Muslims, since Christians, Jews and Muslims worship the same God, albeit that Jews and Muslims do not understand the Trinity nor the Incarnation, but it does not make him a different god. It’s an incomplete or imperfect understanding of God. Therefore, you will see the Holy Father pray along with Protestants, Jews and Muslims, as well as other saintly people.
Partiicpating in Protestant rituals is a little tricky. There is nothing wrong with visiting a Protestant community and praying with them. We often do it when we go to a funeral service, a wedding or even a Baptism, if they have a special Rite of Baptism. These are very special occasions and these are rituals that we have in common: marraige, Baptism and funerals. A Catholic does not need to attend a Protestant service on a regular basis, because everything that he will find in such a service + more is already found in the mass. It’s kind of silly to attend mass and regularly attend a Protestant church just to pray with Protestants.
Other opportunities present themselves to pray together. I work in pro-life ministry. We work very closely with many Protestants, Orthodox Christians, Orthodox Jews and Muslims, because all oppose abortion. We pray together outside of abortion clinics. It’s always funny, because the Catholics always pray the Rosary. It never fails that one of the non-Catholics comes over and joins us in the rosary, especially the Protestants. The Jews and Muslims shy away from it, because of the msyteries and because we say “Mother of God”. That’s a stumbling block for them. But they are always very respectful while we pray the rosary in front of these slaughter houses. We’re very respectful as they pray. It’s actually eaiser for us to join them, because there is nothing in their prayers that is a stumbling block for Catholics. They Muslims don’t pray to Mahhamed. The Jews don’t use audible prayers. The Protestants pray to Christ. That’s an example of shared prayer with non-Catholics.
I hope that helps.
Fraternally,
Br. JR, OSF
