Why Is Pork Haram?
Question

I am an Arab living in Malta and I want to know the reason why pork is forbidden, because my friends at work are asking me about that.
Praise be to Allah.Importance of accepting the rules of Shari`ah
The basic principle for the Muslim is that he obeys whatever Allah enjoins upon him, and refrains from whatever He forbids him, whether the reason behind that is clear or not. 
It is not permissible for a Muslim to reject any ruling of Shari’ah or to hesitate to follow it if the reason behind it is not clear. Rather he must accept the rulings on halal and haram when they are proven in the text, whether he understands the reason behind that or not. Allah says (interpretation of the meaning): 
“It is not for a believer, man or woman, when Allah and His Messenger have decreed a matter that they should have any option in their decision. And whoever disobeys Allah and His Messenger, he has indeed strayed into a plain error.” [al-Ahzab 33:36] 
“The only saying of the faithful believers, when they are called to Allah (His Words, the Quran) and His Messenger, to judge between them, is that they say: ‘We hear and we obey.’ And such are the successful (who will live forever in Paradise).” [al-Nur 24:51]
Why is pork haram?
Pork is forbidden in Islam according to the text of the Quran, where Allah says (interpretation of the meaning): 
“He has forbidden you only the Maytah (dead animals), and blood, and the flesh of swine…” [al-Baqarah 2:173]
It is not permissible for a Muslim to consume it under any circumstances except in cases of necessity where a person’s life depends on eating it, such as in the case of starvation where a person fears that he is going to die, and he cannot find any other kind of food, based on the shar’i principle: “In cases of necessity, haram things are permitted.” 
There is no mention in the Shar’i texts of a specific reason for the prohibition on pork, apart from the verse in which Allah says (interpretation of the meaning): “for that surely, is impure” [al-An'am 6:145]. 
The word rijs (translated here as ‘impure’) is used to refer to anything that is regarded as abhorrent in Islam and according to the sound human nature (fitrah). This reason alone is sufficient. 
And there is a general reason which is given with regard to the prohibition on haram food and drink and the like, which points to the reason behind the prohibition on pork. This general reason is to be found in the verse in which Allah says (interpretation of the meaning): 
“He [i.e., the Prophet (peace and blessings of Allah be upon him)] allows them as lawful At-Tayyibat (i.e. all good and lawful as regards things, deeds, beliefs, persons and foods), and prohibits them as unlawful Al-Khabaith (i.e. all evil and unlawful as regards things, deeds, beliefs, persons and foods).” [al-A'raf 7:157]
The general meaning of this verse includes the reason for the prohibition on pork and it may be understood that in the Islamic viewpoint, it is included among the list of things that are evil and unlawful (al-khabaith). 
What is meant by al-khabaith here is all things that will harm a person’s health, wealth or morals. Everything that leads to negative consequences in one of these important aspects of a person’s life comes under the general heading of khabaith. 
Scientific and medical reasons for prohibiting pork
Scientific and medical research has also proven that the pig, among all other animals, is regarded as a carrier of germs that are harmful to the human body. Explaining all these harmful diseases in detail would take too long, but in brief we may list them as: parasitic diseases, bacterial diseases, viruses and so on.  
These and other harmful effects indicate that the Wise Lawgiver has only forbidden pork for a reason, which is to preserve life and health, which are among the five basic necessities which are protected by Shari’ah. 
For more, please see these answers: 751 and 26792  
And Allah knows best.