The importance of the Holy Book of Glory in the Glorious Church is akin to the Bible's role in Christianity.
While it may have seemed that Duke St. Chapman was assisting the Church in spreading the gospel by promoting the Holy Book of Glory and raising it to the highest authority, a deeper thought reveals that this move was actually aimed at weakening the Church's influence and even commandeering its authority.
If the Empire's citizenry can hear the good news from interpreters assigned by Lords, why should they specifically seek a priest?
If the path to redemption from the Lord of Glory is written in the Holy Book of Glory, why should they pray and confess in church?
If the Holy Book of Glory is the supreme authority, should one still comply when the Pope's decrees contradict it?
Subtly, the influence of the Church in the people's spiritual domain was steadily weakened.