Those who receive the sacrament of Holy Orders -- as a deacon, priest or bishop -- are consecrated in Christ's name "to feed the Church by the word and grace of God."
Through the Sacrament of Holy Orders, bishops and priests are given a special role in carrying out this mission. They exercise a ministerial priesthood. Deacons also receive a special grace through ordination and are called to assist the ministry of bishops and priests [CCC], nos. 1547, 1554
The bishop receives the fullness of the sacrament of Holy Orders. As successors of the Apostles… bishops share in the apostolic responsibility and mission of the whole Church under the authority of the Pope, successor of St. Peter. [CCC], no. 1594
Through their ministry, priests are called, in imitation of Christ, to “preach good news to the poor . . . proclaim release to the captives and recovery of sight to the blind, to set at liberty those who are oppressed, to proclaim the acceptable year of the Lord (Lk 4:18-19)” (Pope John Paul II, Pastores Dabo Vobis [I Will Give You Shepherds], no. 11).
Deacons, too, are ordained to imitate Christ in his ministry of service and charity to the poor and needy in the community. Deacons are ordained for tasks of service of the Church…ordination confers upon them important functions in ministry of the word, divine worship, pastoral governance, and service of charity… [CCC] no. 1596