"the removing of those things that are shaken"
A fresco showing the conversion of St Paul painted by Michelangelo
Public DomainA fresco showing the conversion of St Paul painted by Michelangelo

This quotation comes from St Paul's Epistle to the Hebrews (12:27) in the Bible.

St Paul was one of the driving figures of the early Church. He set down many of the rules and principles by which the Church operates, and his teachings tend to be favoured by more conservative, traditional thinkers like Angel's father.