The verse says...
The verse says: "Tell the believing men to lower their gaze and guard their modesty...." The Arabic word /yaquddu/ is derived from the word 'Qazz', which originally means to decrease or to lessen. In many cases it is used in the sense of: to lower voice or to lessen looking. Thus the verse does not say that the believers must close their eyes, but it says that they must lessen or shorten their looking.
This is a delicate way of speaking, because if a man really wants to close his eyes when he sees a woman who is related within forbidden degrees, he can no -longer walk, but if he casts down his gaze and does not look at her face and her body,it is as though he has shortened his gaze and has totally deleted the scene, that is forbidden, from the scope of his eyes.
It is worth-studying that the holy Qur'an does not specify the thing that a person must cast down gaze from (so as to say complement of the verb is omitted), in order that it will be a general rule; that is, one must cast down gaze from whatsoever is unlawful to look at. But, with regard to the context of these verses, specially the following verse that mentions veil, it will be clear that it means not looking at women who are related within forbidden degrees (or are marriageable).
The occasion of revelation, mentioned at the beginning, confirms this matter, too. From what was said this matter is understood that the verse does not signify that men must not gaze or stare at women's face so that some people misuse it and say that not staring look is permitted.
However, its purpose is that when a man looks or sees, the scope of his vision is vast, and at the time of entering a woman who is related within forbidden degrees in the scope of his vision, he must cast down his look in a way that the woman exits the scope. It means he does not look at her, but he must see his way and path; and that it is said that the word /qacld/ has been applied with the sense of 'to decrease' means the same.
(Take care) The second command that is mentioned in the verse is to guard ones modesty and to be modest. The Arabic word /farj/ in fact means a split or opening between two things, but in such cases it connotes pudendum. In Persian language, is used instead of it, for keeping its-connotative meaning. The purpose of 'being modest', according to Islamic narrations, is covering the pudendum for not to be seen by others.