It’s often commonly perceived that a central difference between Protestant and Roman Catholic ecclesiologies lies in that the former claims that one’s membership in the church is conditioned upon their union with Christ, whereas the latter tends to argue that one is only united with Christ through their membership in the church. Obviously this is caricature, but it does get at a common sentiment or style often found in various Protestant and Roman ecclesiologies.
But in turning the Roman Catechism again, I noticed something rather different. The Catechism specifically posits “the unity of all [the church's] members with each other as a result of their union with Christ” (789). This is the exact articulation of what is commonly perceived as the “Protestant” instinct, namely to argue that the church’s mutual togetherness is constituted by Christ’s own indwelling of all Christians. In other words, even for the Roman Catechism one does not obtain union with Christ by becoming part of the church, rather through Christ’s act of uniting himself with you, you become part of the community of all those in whom Christ already dwells through the Spirit.