According to gsm arena specs, the Samsung Galaxy A7 (2017) comes with a Corning Gorilla Glass 4 back panel. I assume this is right because the A7 does feature a 3D glass back according to the press release, so I assume Samsung took some measured to protect the phone by using a hardened material, and I already know that the previous Galaxy A7 (2016) has Corning Gorilla Glass 4 and the new one has it as well, so I believe that the same CGG4 is used for the rear as well as mentioned in gsmarena Galaxy A7 (2017) specification page, but it's not mention in the official press release that the back panel uses Gorilla Glass 4.
Gorilla Glass 4 is not the most advanced and hardest protection, there is already Gorilla Glass 5, and by the way, the Samsung Galaxy Noet 7 was the first phone to use Gorilla Glass 5. Gorilla Glass 4 still provided very good protection against scratches and sharp contact damage as well as improved drop performance and superior surface quality compared to previous generation Gorilla Glass. So this glass will provide greater damage resistance and help protect your Samsung Galaxy A7 (2017) smartphone from being damaged. I personally always prefer using a protective case for any phone that I buy, and I also prefer to also use a glass cover for the screen, just to make sure that my phone isn't damage and I can sell it for a good price when I want to upgrade.