Simplify the following text for a Grade 9 native English-speaking person.
Original: Religious services for the whole Order are held quadrennially ; new Knights and Dames Grand Cross are installed at these services .
Simplified: Religious services for the whole Order are held every four years . New Knights and Dames Grand Cross are ` installed ' at these services ( this means that they are officially appointed and make an oath of loyalty to the Sovereign ) .