The Catechism of St. Robert Bellarmine: Chapter I
Student. So that I may grasp the understanding of Christian doctrine that is necessary for salvation, I especially long for you to tell me: what is Christian doctrine?
Teacher. Christian Doctrine is like a short compendium, or a summary of all those things that Christ our Lord taught when He showed us the way of eternal salvation.
S. What principal parts of this doctrine are most important?
T. There are four, namely, the Apostle’s Creed, the Lord’s Prayer, the Ten Commandments and the Seven Sacraments.
S. Why are there only four parts and not a great many more, or fewer?
T. Because the first three principle parts correspond to the virtues of Faith, Hope, and Charity. The Apostle’s Creed is necessary for faith itself since it teaches us those things that we ought to believe. The Lord’s Prayer is necessary for hope itself, as you see it proposes to us what is to be hoped for. The Ten Commandments teach us those things that are necessary for charity, what we must do to please God. Lastly, the Seven Sacraments are necessary because they are the instruments whereby we might recoup and preserve the virtue which we already said was necessary to salvation.
S. Would you give a parable through which I may better understand the necessity of these parts?
T. St. Augustine uses a parable about a house. Just in the way that the placement of a foundation is necessary to the structure of a house, then from there the building of the walls, and next the construction of the roof and different hardware; so also in the structure of salvation it is necessary to lay the foundation of faith, the walls of hope and the roof of charity, and lastly, the hardware which is the holy Sacraments themselves.
– Lucas G. Westman