"Christ is the light of humanity; and it is, accordingly, the heart-felt desire of this sacred Council, being gathered together in the Holy Spirit, that, by proclaiming his Gospel to every creature, it may bring to all men that light of Christ which shines out visibly from the Church." These words open the Second Vatican Council's Dogmatic Constitution on the Church. By choosing this starting point, the Council demonstrates that the article of faith about the Church depends entirely on the articles concerning Christ Jesus. The Church has no other light than Christ's; according to a favorite image of the Church Fathers, the Church is like the moon, all its light reflected from the sun.
Source: Catechism of the Catholic Church (Vatican.va)