3353
"O you who believe, do not enter the homes of the prophet unless you are invited to a meal, without you forcing such an invitation. But if you are invited, you may enter. And when you finish eating, you shall leave, without staying to wait for a narrative. This used to bother the prophet, and he was shy to tell you. But God does not shy away from the truth. And if you ask his wives for something, ask them from behind a barrier. This is purer for your hearts and their hearts. And it is not for you to harm the messenger of God, nor that you should marry his wives after him. This is indeed a gross offence with God."

336
"The prophet is closer to the believers than themselves, and his wives are mothers to them. And the decree of God to the believers and the emigrants is that before they help their relatives, they have taken care of their own families first. Such has been decreed in the Book."

3353 instructs the prophet's contemporaries to address the his wives from behind a barrier and at the same time 336 states that his wives are like mothers to the believers. Although I understand the latter to be metaphorical, I certainly do not ask something of my own mother from behind a barrier.

Does anyone know the reasoning behind this injunction? My understanding is that because among the believers there may be those with enmity toward the prophet and his family and this injunction is an overall protective measure for his wives. Also, because 3353 begins talking about the prophet's houses, it may be that those who visit these houses to ask the prophet's wives something are asked to do so behind a barrier so that the prophet's wives, who may have had a lot of inquisitors given their husband's status, would not be inconvenienced by clothing with acceptable attire and accommodating every guest who showed up at the door.