Why must a girl wear the hijab and not show any part of her body except to unmarriageable kin (mahrams) and her husband, and what will happen if she wears modest attire but it is not a hijab?

The hijab is an obligatory duty upon a girl as soon as she reaches puberty, in compliance with Allah's command. Disobeying Allah's command leads one into clear violation of His commands and prohibitions, and may result in falling into temptation and severe torment. Furthermore, the hijab has great benefits, such as protecting and safeguarding women from suspicious gazes and harassment. Let the questioner fear Allah and adhere to His commands to taste the true sweetness of faith.