The phrase "to protect the glass" means to keep the glass safe and free from damage or harm.
Sentences with «to protect the glass»
UV - protected glass doors that keep out the sun's rays. (idealhome.co.uk)
The removable glass insert, when assembled with the translucent plastic sleeve, helps protect the glass. (5phases.com)
What's nice about this product is that it comes with a silicone sleeve to help improve your grip, reduce heat transfer and,... MORE of course, protect the glass bottle. (thespruce.com)