from Mark Noll's Is the Reformation Over?:

What, then, do Catholics believe the church is? In working through the Apostles' Creed, the Catechism explains the creed line by line, coming eventually to the statement, "I believe in the holy catholic church." It then describes the church with biblical images familiar to Protestants and held in common by both groups. The church is the people of God, the body of Christ, and the temple of the Holy Spirit. [781-810]

... in drawing insights from great thinkers of the Christian past, the Catechism takes the image one step beyond a Protestant understanding. In doing so, a long list of ecclesiological differences falls into place. An unusually clear statement of the Catholic position is found in the Catechism's 795th paragraph:

Let us rejoice then and give thanks that we have become not only Christians, but Christ himself. Do you understand and grasp, brethren, God's grace toward us? Marvel and rejoice: we have become Christ. For if he is the head, we are the members; he and we together are the whole man. . . . The fullness of Christ then is the head and the members. But what does "head and members" mean? Christ and the Church.230

Our redeemer has shown himself to be one person with the holy Church whom he has taken to himself.231

Head and members form as it were one and the same mystical person.232

A reply of St. Joan of Arc to her judges sums up the faith of the holy doctors and the good sense of the believer: "About Jesus Christ and the Church, I simply know they're just one thing, and we shouldn't complicate the matter."233

Christ and his church are one! This basic confession explains why Catholics can offer salvation through baptism into the church. [Noll's footnote: Ibid., 354, par. 1266. The Catechism says repeatedly that salvation comes from God alone (not baptism itself). See pars. 169, 846, 1584.] It is why the pope (as the vicar of Christ) can speak without error in matters of faith and morals. It is why Ignatius, who died in 110, could say that only priests in connection with a bishop, in connection with the pope, can offer valid sacraments. It is why Protestants may not share a Catholic Eucharist. To do so would acknowledge the authority of the pope as representing Christ through his church. It is why Cyprian, who died in 258, could say, "No one can have God as Father who does not have the Church as Mother." It is why Mary is called the mother of the church; she is the mother of Christ. It is why the church can interpret the keys given to Peter as authority to forgive sins. It is why sin against God is also sin against the church and requires reconciliation to both. In a word, ecclesiology represents the crucial difference between evangelicals and Catholics.

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