To answer this question about wearing Hijab , we should first understand why God has sent down religion to man and why He orders man what to do and what to avoid.
Imagine a person who invents an electronic device, for example, a computer; he knows how the computer should be used to give the best outcome. Therefore, there is always a manual coming with the computer that tells us how to use it for a better result. So the user uses the manual to keep the computer safe and productive.
God has created man, and He knows what is good and what is harmful to him/her. He sent the religion and the Quran as a guide for human beings. Following the instructions in the book will lead to the useful, peaceful and productive life of a human.