This is a metaphorical expression in English. When you "hold a mirror up to" something it means you are going to examine it and think about it. If you look at words in English it may make more sense. The purpose of a mirror is to "reflect" right? In English the word "reflect" can not just mean "bound back light" but it can also mean "think about deeply" or "consider." Therefore, when you are "reflecting on linguistics" it means you're thinking about linguistics deeply and examining it's nature more closely. Does that make sense? :-)

hello can you add my SKYPE : frank.liangyong.101

Hi, I'd like to be language partners on italki. I'm Ron in New York, USA. I'm happy to help you improve your spoken English. If you need help, please add me to your Skype: ron.jenkins86 And if you want a new friend, lets be friends! :) Thanks and see you soon!