What, from the Catholic point of view, constitutes the unity of the church?

The Church is one, because of its origin, the unity of the one God, the Father, Son and Holy Spirit in the Trinity. It is one, because of its founder, Jesus Christ, and it is one because of its soul, the Holy Spirit who dwells in the believer and who fulfills and guides the whole Church.

From its beginning there has been much diversity within the Church. This originates from the diversity of God’s gifts, but also from the diversity of the people who receive those gifts. This diversity among its members arises either by reason of their duties, as is the case with those who exercise the sacred ministry for the good of their brethren, or by reason of their condition and state of life, as is the case with those many who enter the religious state and, tending toward holiness by a narrower path, stimulate their brethren by their example. Moreover, within the Church particular Churches hold a rightful place; these Churches retain their own traditions, without in any way opposing the primacy of the Chair of Peter, which presides over the whole assembly of charity (cf. LG: http://www.ewtn.com/library/councils/v2church.htm, German: http://www.stjosef.at/konzil/LG.htm)

This rich diversity does not oppose the unity of the Church, but sin and its consequences constantly burden and threaten this gift of unity " (KK 814).

What are the ties of unity of the Church? First of all, it is love, “the bond of perfection“ (Colossians 3:14). The unity of the church is also ensured with the following visible ties:

- the commitment to one and the same apostolic faith ;
- celebrating worship together, especially the sacraments
- apostolic succession, i.e. the continuous succession of Bishops and Priests going back to the Apostles, which through the sacrament of consecration sustains brotherly harmony in the family of God.

"This is the one Church of Christ … which our Savior, after His Resurrection, commissioned Peter to shepherd, and him and the other apostles to extend and direct with authority…. This Church constituted and organized in the world as a society, subsists in [Lat: subsistit in] the Catholic Church, which is governed by the successor of Peter and by the Bishops in communion with him” (LG 8).