The Lord promises the disciples His Holy Spirit [...] Jesus told his disciples everything, and God can give no more than himself. In Jesus, God gave us his whole self, that is, he gave us everything. As well as or together with this, there can be no other revelation which can communicate more or in some way complete the Revelation of Christ. In him, in the Son, all has been said to us, all has been given.
But our understanding is limited: thus, the Spirit's mission is to introduce the Church, in an ever new way from generation to generation, into the greatness of Christ's mystery. The Spirit places nothing different or new beside Christ; no pneumatic revelation comes with the revelation of Christ - as some say -, no second level of Revelation.
No: "He will have received from me...", Christ says in the Gospel (Jn 16: 14). And as Christ says only what he hears and receives from the Father, thus the Holy Spirit is the interpreter of Christ. "He will have received from me". He does not lead us to other places, far from Christ, but takes us further and further into Christ's light. Consequently, Christian Revelation is both ever old and new. Thus, all things are and always have been given to us. At the same time, every generation, in the inexhaustible encounter with the Lord - an encounter mediated by the Holy Spirit - always learns something new.
[Pope Benedict, homily possession Cathedra Romana 7 May 2005]