That others can see in you as easily as you think you can see out. That glass provides reflection and much of what you think you see in others is really a reflection of what you see in yourself. That no matter how pretty you dress up your glass, no matter how you display it, at the end of the day it matters most what you put on the inside. What you pour into your glass house.
Then when the stones come and they will, your glass house will stand, reflecting your true beauty inside and out.