The Church knows that she is joined in many ways to the baptized who are honored by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter.
Those who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church.
With the Orthodox Churches, this communion is so profound that it lacks little to attain the fullness that would permit a common celebration of the Lord's Eucharist.
— Catechism, No. 838