Modesty is one of the most praiseworthy characters of a Muslim.
It is reported in a hadith that Prophet peace be upon him said:
"Modesty (Al-Haya') is a branch of Faith."
Sunan an-Nasa'i 5006 (Sahih by Darussalam)
And in another hadith.
The Prophet (ﷺ) passed by a man who was admonishing his brother regarding Haya' (pious shyness from committing religious indiscretions) and was saying, "You are very shy, and I am afraid that might harm you." On that, Allah's Messenger (ﷺ) said, "Leave him, for Haya' is (a part) of Faith."
Sahih al-Bukhari 6118
Hijab is an important aspect of modesty, that sisters should maintain. it is for protecting their chastity and seeking the pleasure of Allah by following His command.
Allah says in Quran
وَقُل لِّلْمُؤْمِنَـٰتِ يَغْضُضْنَ مِنْ أَبْصَـٰرِهِنَّ وَيَحْفَظْنَ فُرُوجَهُنَّ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا مَا ظَهَرَ مِنْهَا ۖ وَلْيَضْرِبْنَ بِخُمُرِهِنَّ عَلَىٰ جُيُوبِهِنَّ ۖ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا لِبُعُولَتِهِنَّ أَوْ ءَابَآئِهِنَّ أَوْ ءَابَآءِ بُعُولَتِهِنَّ أَوْ أَبْنَآئِهِنَّ أَوْ أَبْنَآءِ بُعُولَتِهِنَّ أَوْ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ أَخَوَٰتِهِنَّ أَوْ نِسَآئِهِنَّ أَوْ مَا مَلَكَتْ أَيْمَـٰنُهُنَّ أَوِ ٱلتَّـٰبِعِينَ غَيْرِ أُو۟لِى ٱلْإِرْبَةِ مِنَ ٱلرِّجَالِ أَوِ ٱلطِّفْلِ ٱلَّذِينَ لَمْ يَظْهَرُوا۟ عَلَىٰ عَوْرَٰتِ ٱلنِّسَآءِ ۖ وَلَا يَضْرِبْنَ بِأَرْجُلِهِنَّ لِيُعْلَمَ مَا يُخْفِينَ مِن زِينَتِهِنَّ ۚ وَتُوبُوٓا۟ إِلَى ٱللَّهِ جَمِيعًا أَيُّهَ ٱلْمُؤْمِنُونَ لَعَلَّكُمْ تُفْلِحُونَ
“And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent (like both eyes for the necessity to see the way, or outer palms of hands or one eye or dress like veil, gloves, headcover, apron), and to draw their veils all over Juyoobihinna (i.e. their bodies, faces, necks and bosoms) and not to reveal their adornment except to their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons, or their brothers or their brother’s sons, or their sister’s sons, or their (Muslim) women (i.e. their sisters in Islam), or the (female) slaves whom their right hands possess, or old male servants who lack vigor, or small children who have no sense of feminine sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allaah to forgive you all, O believers, that you may be successful”
Surah An-Nur 24:31
so according to Him, it is obligatory for women to wear hijab when going outside or when in presence of non-mahram.
Hazrat Aisha may Allah be pleased with her, said:
May Allah have mercy on the early immigrant women. When the verse "That they should draw their veils over their bosoms" was revealed, they tore their thick outer garments and made veils from them.
Sunan Abi Dawud 4102
But it is not just the outer hijab, rather there is also the inner hijab.
Women must protect their chastity and honors, by avoiding free mixing with non-mahram and making friends with them, they also should lower their gaze down, they also should avoid softening their voices in their presence too as well.
Unfortunately, there are still many women who wear hijab yet they free mix with nonmahram males and becoming their friends. this is not the way of hijab.
As for the men. They still have to cover their awrah, which is between navel and knees, and lowering their gaze down, avoiding any unnecessary contact with non-mahram or being friends or in Zina relationship with them. Unfortunately, torn clothing which has become popular among clothing fashions is worn by the men, revealing their awrah without feeling ashamed. This is unIslamic.
Parents should teach their children, sons, and daughters to cover their awrah.
Hazrat Saladin, once said:
If you want to destroy any nation without war, make adultery and nudity common in the young generation.
And Allah knows best.