What is the degree of sin in not wearing the khimar?

Immodest display (tabarruj) and abandoning the hijab are among the major sins (kaba'ir adh-dhunub), because it is a violation of the command of Allah and His Messenger. Allah the Almighty forbade immodest display and commanded the hijab, saying: "And do not display yourselves as [was] the display of the former times of ignorance" and "O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments." As also stated in the noble Hadith, among the people of Hellfire are "women who are clothed yet naked, inclining [to evil] and causing [others] to incline."