Catholicism believes in the necessity of the church. Church is a word we use for the building where Christians worship, but it is also the assembly of believers, from the Greek word ekklesia.
So in one sense, the church is where Christians pray and at the same time the church is the actual gathering (congregation, assembly, community) of people, since Jesus said “where two or more are gathered in my name, there shall I be in their midst.”
Jesus himself used the word “church” in the Gospel, especially in Matthew 16 when he said to Simon Peter, “I will build my church.” Catholics regard the church as being founded by Christ; therefore it is His church. It is not the pope’s church, not the bishop’s church, and not the priest’s church. It is not even the people’s church. It is Christ’s church.
The main purpose of the church is to continue the work and mission of Christ. Jesus was priest, prophet, and king who sanctified, taught, and governed in his work to redeem and save mankind. His church continues those three-fold missions of sanctifying, teaching, and governing. The church sanctifies by celebrating the seven sacraments instituted by Christ Himself.
The church teaches through her magisterium (the official teaching authority of the pope and the bishops in union with him). The church governs and shepherds through the hierarchy, the chain of command from pope down to pastor.
Jesus entrusted the seven sacraments to the church to protect and to faithfully celebrate. It was the church to whom Jesus entrusted divine revelation, both sacred scripture and sacred tradition. While there is an institutional dimension to the church because of its external structure (laws, customs, vocabulary, leadership), the spiritual is primary. The church is often called the primordial sacrament. While not one of the seven sacraments, the church is like a sacrament in that it was founded by Christ and also communicates grace (through the administering of the sacraments).
Saint Paul uses the analogy of a body to describe the church. Jesus is the head; we are the members, like our hands, fingers, toes, feet, eyes, ears, lungs, and heart are members of our physical bodies. Pope Pius XII elaborated further by calling the church the Mystical Body of Christ. A physical body is limited to time and space, but a mystical body stretches from the past through the present toward the future.
The Gospel of Matthew describes Christ’s Second Coming and the Final Judgment as akin to a shepherd separating sheep from goats. The “sheep” go on the right and enter heaven; the “goats” go to the left and are condemned to hell. But what determines whether one is considered a sheep or a goat? In essence Jesus asks: “When I was hungry, did you give me something to eat? When thirsty, something to drink? Naked, and something to wear? Sick or imprisoned, and visit me? Homeless, and give me shelter?” The message here is that whenever a believer does something good for another person, he does it for Christ, since all the members compose the one mystical body of Christ, the church—the people of God united in baptism. Likewise, if believers neglect anyone’s needs, they neglect Christ.
The church on earth is sometimes called the Pilgrim Church or the Church Militant. Pilgrims are people who are on a journey; in the spiritual realm, this means that members of the church are on a journey from this world to the next. The word “militant” in “Church Militant” does not mean the church is hostile to nonmembers; it is not making war between Catholics and Protestants, or Christians and Jews or Muslims. It is militant in that the church is at war with sin and Satan. Racism, bigotry, terrorism, exploitation of women and children, pornography, abortion, euthanasia, sexual licentiousness, lust, greed, anger, and sin in all its forms are the enemies of the church; the weapons to fight this war on sin are truth, grace, mercy, and justice.
The term Church Suffering refers to the members of the church who are dead but in Purgatory, awaiting the glory of heaven. The Church Triumphant is all the saints and angels now in heaven. The Catholic Church therefore sees herself as essential to saving souls since she is the caretaker and guardian of the fullness of grace (all seven sacraments) and the fullness of truth (divine revelation through both sacred scripture and sacred tradition). The church is not just an organization or association. It is an organic community of living beings whom we call the children of God.
Often called Holy Mother Church, the image of mother that comes from the natural realm is mirrored in the supernatural. Our physical mothers gave birth to us; the mother church gives members their second birth by baptism. Our mothers nursed us from their breasts; the mother church feeds the body with the food from heaven, the Holy Eucharist (body and blood of Christ). Our mothers healed us when we were sick; the mother church heals through the sacrament of anointing. Our mothers taught us; mother church teaches through her magisterium. Our mothers disciplined us; the mother church has rules and laws for our benefit. Catholicism sees “church” as being much more than a building or an institution; it is the living, teaching, sanctifying, and shepherding mission of Christ continued through the ages. Membership has its privileges and its obligations.
A final useful analogy is to think of the church as a ship sailing toward the shore of heaven with the pope as captain and the baptized as crew. You can get there swimming alone, but a much easier and better way is to be on board the boat, helping each other.