Amatul Rahmân Omer:
Surely, those who have believed and have emigrated and strove hard with their possessions and their persons in the cause of Allâh (- the Muhâjirs), and who have given (them) refuge and helped (- the Ansâr), are friends one to another. But you are not responsible for the protection of those who have believed but have not emigrated until they do emigrate. However if they seek your help in (the matter of) faith, then it is binding upon you to help them except against a people between whom and yourselves is a treaty. Indeed, Allâh knows well all that you do.