Unclean foods, such as pork, represented sin for example. The sin which the people should avoid to maintain holiness before God. To believe that such a thing as pork meat is unclean in itself is a pagan superstition which it is useful for Islam to maintain as all superstitions are useful to hold power over men. Islam has always held that it is better for Muslims to live separately. Mohammed showed this by leaving Mecca and forming an isolated community of Muslims. This is politically astute for a community that devotes itself to jihadic conquest.
The temple was holy and off bounds to all but the priests and levites to show that God was holy and the people were sinful and thus unclean to come near to the holy God Jehovah.
Bodily discharges made the people unclean to approach the holy God Jehovah in his temple. They symbolized the sinful nature of man from which uncleanness flows irrevocably and continuously from his sinful nature.
Jesus healed people by touching and coming close to people who were unclean according to the law. Lepers for example. He thus showed that sickness is one aspect of the curse which is over all men alike and that all men are unclean before God because of their sinful deeds.