I'm a Muslim, and I practice the basics of Islam moderately and every day. I want to know what exactly was hijab created for, why I have to wear it and why it is compulsory. I grew up wearing it, but I'm not seeing why I have to wear for what I was told "to differentiate myself, repel harassment and be modest". I can dress modestly without wearing hijab and it doesn't prevent harassment for me (whether I'm wearing full Islamic clothing or everyday jackets and skirts). I want to understand why I have to wear hijab and why I shouldn't take it off before I feel like I don't want to wear it at all.
This is very difficult question to answer. There are two ways to approach it.
One is the more conservative reply and echoes what sister Rebeca has said. And that is that the opinion of all the classical scholars seems to be that hijab is mandatory. It is a command of Allah which must be followed without questioning why. "Why" can be a dangerous path to follow. Do we ask why we pray 5 times a day or why maghrib is 3 rakats or why we have to wipe over the socks and not under?
We just have to believe that this is what our Creator and Lord wants from us so it is a command that must be followed without question. That is what Islam means, submission. You have to think "O Allah, this thing you are asking me to do is not easy and it doesn't make much sense to me, but I trust that you know more than I do what is best for me, so I submit to what you have commanded. I do this out of love for you hoping for your mercy and reward in this world and the next".
That is the answer from the more conservative in me who was raised as a student of knowledge of mainstream Islamic scholarly thinking.
But the reformist in me who realizes the world we live in asks "Just because the classical scholars who lived in a world very different from ours, and lets face it, a more male chauvinistic world, had this opinion, does that mean it is the correct opinion for today? Could it be the ruling of Allah for sisters today is different? Could they still dress modestly without observing full hijab (mainly covering the hair)?" I don't know, these are questions that today's scholars need to be asking.
But if it were my daughter, I would advise her to be on the side of caution with her Lord. This world is short and it is a test. Allah knows best.