Lumen Gentium 3
The Son, therefore, came, sent by the Father. It was in Him, before the foundation of the world, that the Father chose us and predestined us to become adopted sons (and daughters), for in Him it pleased the Father to re-establish all things.(cf Eph. 1, 4-5 and 10) To carry out the will of the Father, Christ inaugurated the Kingdom of heaven on earth and revealed to us the mystery of that kingdom. By His obedience He brought about redemption. The Church, or, in other words, the kingdom of Christ now present in mystery, grows visibly through the power of God in the world. This inauguration and this growth are both symbolized by the blood and water which flowed from the open side of a crucified Jesus,(cf Jn. 19, 34) and are foretold in the words of the Lord referring to His death on the Cross: "And I, if I be lifted up from the earth, will draw all things to myself".(cf Jn. 12, 32) As often as the sacrifice of the cross in which Christ our Passover was sacrificed, is celebrated on the altar, the work of our redemption is carried on, and, in the sacrament of the eucharistic bread, the unity of all believers who form one body in Christ (cf 1 Cor. 10, 17) is both expressed and brought about. All (human beings) are called to this union with Christ, who is the light of the world, from whom we go forth, through whom we live, and toward whom our whole life strains.
This section is super-rich and would, by itself, be sufficient for an evening's thoughtful discussion. First, our kinship in the Trinity is mentioned in close connection with the founding of the Church. In other words, the Church is neither democracy nor autocracy, but a family.
Note the quick phrase definition of the Church: "The Kingdom of Christ now present in mystery." We cannot ever hope to wrap our minds around the full reality of what the Church is and what it means. Enough to say it is founded in a familial relationship with the Father and with the Son. Enough also to say that its function and mission is inevitably intertwined with the Paschal Mystery. Enough indeed to underscore the importance of the celebration of the Eucharist in both defining the Church and strengthening its membership for participation in the mission of Christ.
Go ahead and read it for yourself: