“And when you ask them (i.e. Prophet’s wives) for something, then ask them from behind a veil (Hijaab).” [Surah Al-Ahzaab: 53]
Even though the ones intended by this verse were the wives of the Prophet, the verse is general. So the wording in the verse is specific for the Prophet’s wives, while its meaning is universal for all women since the Prophet’s wives are the role-models for the believing women. Allaah explains this thoroughly in His next statement, where He says:
ذَلِكُمْ أَطْهَرُ لِقُلُوبِكُمْ وَقُلُوبِهِنَّ
“That is purer for your hearts and their hearts.” [Surah Al-Ahzaab: 53]
Allaah ordered that the women be asked from behind a Hijaab. What is meant by the word Hijaab is: Anything that covers a woman whether a garment, a wall, a door or any other object that can be used to screen a woman from a man when he is talking to her or asking her about something or handing her something. All of these should be done from behind a Hijaab, i.e. from behind a screen or covering. So he should not make any contact with her while she is unscreened or lacking covering and exposed. Rather, she must be behind a screen that covers her, regardless if it is her garment, her door, a wall or so on. This is since this is “purer for your hearts and their hearts” from temptation. If women screen themselves by way of a Hijaab and the gaze of men does not fall upon them, the hearts of both the men and women will be saved from temptation and enticement. This is clearly visible in the Muslim societies that strictly adhere to the Hijaab.
A society that strictly adheres to the Hijaab is preserved from the corruption of morals. In fact, it is the lack of Hijaab that results in immorality and the temptation of men’s desires. Therefore Allaah’s saying: “That is purer for your hearts and their hearts” contains a basis that is universal for the whole ummah since the Hijaab consists of a purification of the hearts for both men and women in an equal manner. It blocks all the pathways that lead to the corruption of morals.
Source : Advice to the Muslim Woman – Shaykh Saalih bin Fawzaan al-Fawzaan [al Ibaanah Book]