The first Constitution on the Church clarifies that the Council does not consider the Church as a reality closed in on itself, but in reference to Christ. “Christ is the light of peoples, and this sacred Council, met together in the Holy Spirit, ardently desires that the light of Christ, reflected on the face of the Church, should illuminate all men and women…”
In the background we recognise an image from the theology of the Fathers, which sees the Church as the moon, not giving off its own light, but transmitting the light of Christ’s sun. Ecclesiology is shown to be dependent on Christology, and linked to it.
Seeing as no one can speak correctly about Christ, about the Son, without at the same time speaking of the Father, and seeing that we cannot speak correctly about the Father and the Son without listening to the Holy Spirit, the Christological vision of the Church is necessarily broadened into a Trinitarian ecclesiology (LG 2-4). The discourse on the Church is a discourse about God, and only in this way is it correct.
Card. Joseph Ratzinger
L’ecclesiologia della Costituzione Lumen gentium
Nuova Umanità 22 (2000/3-4) p. 396