They were sincere, but sincerely wrong. Salvation is by grace. Grace is unmerited favor. We cannot earn grace, nor do we deserve grace. The Roman Catholic believes that salvation is based on water and works.
Baptismal regeneration is the cornerstone of the Catholic system.
The Church teaches that no one can enter the kingdom of heaven unless he or she is baptized. The source of Catholic faith is the Church. Its object is loyalty to the Church. Therefore, Catholic faith is in itself. The Christian, however, knows that salvation is based on Christ's work alone, a finished work to which nothing can be added.