The Roman Catholic Church believes that the Rock on which Jesus builds his church was the Apostle Peter, who allegedly was the first Pope or Bishop of Rome. Subsequently, all the Popes have been the spiritual descendants of Peter.
The true church is, therefore, all those who acknowledge the headship of the Pope and belong to the Roman Catholic structure.
In Roman Catholic doctrine, God’s grace flows from God through the Pope, through the Cardinals, through the Bishops, through the Priests, and then to the congregation via the sacraments.
To be excommunicated from the Roman Catholic Church is to endanger your immortal soul.