What makes being Catholic different from being part of any other organization that does good works?
In essence, we don’t have a choice but to do good. Everything Christians do is a response to God who first began that good work in us. Those who seek to be baptized are simply responding to God who “sought and summoned them in many ways” (Rite of Christian Initiation of Adults, #53). By being baptized, we are essentially changed from being an isolated body moving by our own will to being a part of the Body of Christ, in whom “we live and move and have our being” (Preface for Ordinary Time VI). With St. Paul we say, “I have been crucified with Christ; yet I live, no longer I, but Christ lives in me” (Gal 2:19-20). The life we live is the life of Christ who continues his work on earth through the mission of the Church.
Vatican II’s Decree on the Apostolate of Lay People describes this right and duty of the faithful in this way:
The Church was founded for the purpose of spreading the kingdom of Christ throughout the earth for the glory of God the Father…. All activity of the Mystical Body directed to the attainment of this goal is called the apostolate, which the Church carries on in various ways through all her members. For the Christian vocation by its very nature is also a vocation to the apostolate. No part of the structure of a living body is merely passive but has a share in the functions as well as life of the body: so, too, in the body of Christ, which is the Church. (2)It even goes on to say that “the organic union in this body and the structure of the members are so compact that the member who fails to make his proper contribution to the development of the Church must be said to be useful neither to the Church nor to himself” (2).
Therefore, no one in the Church is ever really a “volunteer” who, as the dictionary says, is one who does a service or participates in a transaction without any legal concern or interest in the matter. By baptism, all Christians are obligated to participate in the work of the Church according to each one’s gifts and abilities.
Does this mean we can’t have volunteer fairs and sign-up sheets? Of course not. But we do need to cultivate better the sense of “right and duty” of discipleship that our baptism brings.
Read "Six Ways to Grow Disciples."