CCC 790 - "Believers who respond to God’s word and become members of Christ’s Body, become intimately united with him: In that body the life of Christ is communicated to those who believe, and who, through the sacraments, are united in a hidden and real way to Christ in his Passion and glorification. This is especially true of Baptism, which unites us to Christ’s death and Resurrection, and the Eucharist, by which “really sharing in the body of the Lord, . . . we are taken up into communion with him and with one another.”
Al who are validly baptised form part of the Body of Christ. If non-Catholics who are baptised were not part of the Body of Christ then we would have to maintain that their baptisms were invalid. We recognise the validity of their baptism, they are part of the Body of Christ.
