Decree on the Apostolate of Lay People
Vatican II 18 November 1965

The Church was founded to spread the kingdom of Christ over all the earth for the glory of God the Father, to make all men partakers in redemption and salvation, and through them to establish the right relationship of the entire world to Christ. Every activity of the Mystical Body with this in view goes by the name of "apostolate"; the Church exercises it through all its members, though in various ways. In fact, the Christian vocation is, of its nature, a vocation to the apostolate as well. ... (n. 2)