9 At all times and in every race God has given welcome to whosoever fears Him and does what is right. God, however, does not make men holy and save them merely as individuals, without bond or link between one another. Rather has it pleased Him to bring men together as one people, a people which acknowledges Him in truth and serves Him in holiness. He therefore chose the race of Israel as a people unto Himself. With it He set up a covenant. Step by step He taught and prepared this people, making known in its history both Himself and the decree of His will and making it holy unto Himself. All these things, however, were done by way of preparation and as a figure of that new and perfect covenant, which was to be ratified in Christ, and of that fuller revelation which was to be given through the Word of God Himself made flesh. "Behold the days shall come saith the Lord, and I will make a new covenant with the House of Israel, and with the house of Judah . . . I will give my law in their bowels, and I will write it in their heart, and I will be their God, and they shall be my people . . . For all of them shall know Me, from the least of them even to the greatest, saith the Lord. Christ instituted this new covenant, the new testament, that is to say, in His Blood, calling together a people made up of Jew and gentile, making them one, not according to the flesh but in the Spirit. This was to be the new People of God. For those who believe in Christ, who are reborn not from a perishable but from an imperishable seed through the word of the living God, not from the flesh but from water and the Holy Spirit, are finally established as "a chosen race, a royal priesthood, a holy nation, a purchased people . . . who in times past were not a people, but are now the people of God". That messianic people has Christ for its head, "Who was delivered up for our sins, and rose again for our justification", and now, having won a name which is above all names, reigns in glory in heaven. The state of this people is that of the dignity and freedom of the sons of God, in whose hearts the Holy Spirit dwells as in His temple. Its law is the new commandment to love as Christ loved us. Its end is the kingdom of God, which has been begun by God Himself on earth, and which is to be further extended until it is brought to perfection by Him at the end of time, when Christ, our life, shall appear, and "creation itself will be delivered from its slavery to corruption into the freedom of the glory of the sons of God". So it is that that messianic people, although it does not actually include all men, and at times may look like a small flock, is nonetheless a lasting and sure seed of unity, hope and salvation for the whole human race. Established by Christ as a communion of life, charity and truth, it is also used by Him as an instrument for the redemption of all, and is sent forth into the whole world as the light of the world and the salt of the earth. Israel according to the flesh, which wandered as an exile in the desert, was already called the Church of God. So likewise the new Israel which while living in this present age goes in search of a future and abiding city is called the Church of Christ. For He has bought it for Himself with His blood, has filled it with His Spirit and provided it with those means which befit it as a visible and social union. God gathered together as one all those who in faith look upon Jesus as the author of salvation and the source of unity and peace, and established them as the Church that for each and all it may be the visible sacrament of this saving unity. While it transcends all limits of time and confines of race, the Church is destined to extend to all regions of the earth and so enters into the history of mankind. Moving forward through trial and tribulation, the Church is strengthened by the power of God's grace, which was promised to her by the Lord, so that in the weakness of the flesh she may not waver from perfect fidelity, but remain a bride worthy of her Lord, and moved by the Holy Spirit may never cease to renew herself, until through the Cross she arrives at the light which knows no setting.
Source: Lumen Gentium (Vatican.va)