Overall meaning : Believers, do not enter houses other than your own until you have asked their owners’ permission and greeted their inhabitants with salutations of peace. That is better for you. We have shown you such good manners so that you may remember them and observe the rules of propriety and decorum. If you find no one in them to give you permission to enter, do not go in until you are given leave. If you ask permission but are told to go back, then go back without taking offense or insisting on entering; going back is purer for you. Allah has knowledge of all your actions, and He will repay you according to them.
However, you will incur no sin if you to enter, without permission, homes that are not the private habitation of a family, such as charitable public inns and shelters for travellers and ruined houses; for these serve a purpose that is useful to you. Allah knows everything you conceal and everything you hide deep within yourselves.