What relationship between the church and nonbelievers did Mystici corporis Christi promote?

In the 1943 encyclical Mystici corporis Christi, Pope Pius XII sought to define the nature of the church and its relationship to nonbelievers.5

In this document, Pius XII explicitly identified the mystical body of Christ with the Roman Catholic Church. This perspective maintained a clear distinction between those inside the church and those outside it, consistent with the traditional theological adage that there is "no salvation outside the church". By defining the church in this way, the encyclical reinforced the boundaries between the Catholic faithful and nonbelievers, emphasizing the church as the one and only worshipping community established by Jesus Christ.1

This approach contrasted with later developments, such as those seen during the Second Vatican Council, where the church moved toward a more universal understanding of its nature, suggesting that all persons are at least potentially members of the church because Christ offered salvation to everyone.21