The truth of salvation in Christ is not a rigid letter that can be preserved in a book. It is a treasure that the Lord gave to the apostles so that their union would be the sure guarantee of their possession of the truth of salvation. The apostles passed this treasure on to the bishops so that they might complete the mission, in their union with the Church - the Body of Christ, where the Holy Spirit works. In doing so, they do not express their own opinion, but the will of the Holy Spirit who dwells in the Church.