Answer:Islam is a system which designs every aspect of human life, morality and ethical rules one of them. There are five essential pillars which every divine religion aims to protect them. Those are religion, life, property, intellect and progeny. Your question is related to the last one. In order to protect progeny God prohibited adultery and allowed marriage so human beings can satisfy natural desires through lawful means as well as the generation is protected. In order to prevent evil results God blocked the means which lead to them from the beginning. For example God said ” Tell the believing men that they should restrain their gaze (from looking at the women whom it is lawful for them to marry, and from others’ private parts), and guard their private parts and chastity. This is what is purer for them. God is fully aware of all that they do.” (24:30) In order to protect Believers from adultery God commanded them to restrain their gaze from looking at the women. The means which lead to fornication or any other indecent behavior starts with looking and intermingling, thus it is a precaution to sit separately and not to look at the face of women.