From Congar (On Ecclesiology)

The pre-conciliar works of the Ressourcement theologians shed an interesting light on our understanding of the Second Vatican Council, especially when we consider the influence that their theological ideas had on the Fathers of the Council:

While there is certainly cause for rejoicing in the present-day return to favour of the title "the People of God" and in the response it shows itself capable of arousing, and while we must of course recognize the importance of the place it occupies in Scripture, it would appear at that we should not choose it as our central concept in ecclesiology, as has been sometimes suggested. It expresses directly one aspect of the Church only, and this, moreover, only from a more or less external point of view -- at any rate, as far as the primary meaning is concerned. This view will also have the advantage of keeping us clear of the danger involved in all those tendencies that wish to make of the Church the invisible society of the Saints and the elect. (Congar, The Splendor of the Church, 106-7)

Personally, I am strongly of the opinion that the fundamental key to understanding the doctrine of the Church in Lumen Gentium is the analogy drawn between the Church and a sacrament:

Christ is the Light of nations. Because this is so, this Sacred Synod gathered together in the Holy Spirit eagerly desires, by proclaiming the Gospel to every creature, to bring the light of Christ to all men, a light brightly visible on the countenance of the Church. Since the Church is in Christ like a sacrament or as a sign and instrument both of a very closely knit union with God and of the unity of the whole human race, it desires now to unfold more fully to the faithful of the Church and to the whole world its own inner nature and universal mission. (Lumen Gentium 1)
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.(98) 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. (Lumen Gentium 9)