Each deacon must be called by God to serve as His deacon. This divine “calling” to serve in the ministry of diaconate is called a vocation. The bishops of the United States describe the mystery of vocation in the follow terms:
“Every Christian vocation is the history of an inexpressible dialogue between God and human beings, between the love of God who calls and the freedom of individuals who respond lovingly to him.” This calling forth from God is marked first in the reception of the sacraments of Christian Initiation. From out of this body of believers Christ then calls some of his disciples, and the Church, discerning their vocational charism, asks the bishop to ordain them to a service of the whole church (National Directory for the Formation of Permanent Deacons, art. 165).
God calls those whom he chooses to each of the ministries of Holy Orders. It is up to each man who is called by God to recognize and respond generously to the Lord’s invitation.