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, for in Him it pleased the Father to re-establish all things. 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, 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". 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 is both expressed and brought about. All men 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.
Source: Lumen Gentium (Vatican.va)