A Christian is asking about the reason for the prohibition on pork
Question

Why does Islam forbid pork, when the pig is one of the creations of God?.
Praise be to Allah.Firstly: 
Our Lord has forbidden eating pork in definitive terms. Allaah says (interpretation of the meaning): 
“Say (O Muhammad): I find not in that which has been revealed to me anything forbidden to be eaten by one who wishes to eat it, unless it be Maytah (a dead animal) or blood poured forth (by slaughtering or the like), or the flesh of swine (pork); for that surely, is impure or impious (unlawful) meat (of an animal) which is slaughtered as a sacrifice for others than Allaah (or has been slaughtered for idols, or on which Allaah’s Name has not been mentioned while slaughtering)”
[al-An’aam 6:145]
By the mercy of Allaah and His kindness towards us, Allaah has permitted us to eat all good things, and He has not forbidden anything but those that are impure. Allaah says (interpretation of the meaning): 
“…he allows them as lawful At‑Tayyibaat (i.e. all good and lawful as regards things, deeds, beliefs, persons and foods), and prohibits them as unlawful Al‑Khabaa’ith (i.e. all evil and unlawful as regards things, deeds, beliefs, persons and foods)”
[al-A’raaf 7:157]
We do not doubt for an instant that the pig is a dirty and filthy animal, and that eating it is harmful to man. Moreover it lives on dirt and filth, and it is something that is off-putting to those of a sound nature who refuse to touch it, because eating it is either a cause or a sign of a person’s oddness. 
Secondly: 
With regard to the physical harm caused by eating pork, modern science has proved a number of things, such as the following: 
‎Pork is regarded as one of the kinds of meat that contain the most cholesterol, an increase of which in the bloodstream leads to an increased likelihood of blocked arteries. The fatty acids in pork are also of an unusual formation, when compared with the fatty acids in other types of food, which makes them more easily absorbed by the body, thus increasing cholesterol levels.
‎Pork meat and pork fat contribute to the spread of cancers of the colon, rectum, prostate and blood.
‎Pork meat and pork fat contribute to obesity and related diseases that are difficult to treat.
‎Eating pork leads to scabies, allergies and stomach ulcers.
‎Eating pork causes lung infections which result from tapeworms, lungworms and microbial infections of the lungs.
The most serious danger of eating pork is that pork contains tapeworms which may grow to a length of 2-3 meters. The growth of the eggs of these worms in the human body may lead to insanity and hysteria if they grow in the area of the brain. If they grow in the region of the heart that may lead to high blood pressure and heart attacks. Another kind of worm that is to be found in pork is the trichinosis worm that cannot be killed by cooking, the growth of which in the body may lead to paralysis and skin rashes. 
The doctors have confirmed that tapeworm disease is regarded as one of the serious diseases that may result from eating pork. It may develop in the small intestine and after several months may grow into a large worm whose body is composed of a thousand segments, with a length of 4-10 meters, which lives alone in the intestine of the infected person and part of it may appear when he defecates. When the pig swallows and ingests its eggs, they enter the tissues and muscles in the form of larvae sacs containing fluid and the head of the tapeworm. When a person eats infected pork, the larva turns into a complete worm in the intestine. These worms cause weakness and vitamin B12 deficiency, which leads to a specific type of anaemia, which may in turn cause nervous problems. In some cases the larvae may reach the brain, causing convulsions, increased pressure within the brain, epilepsy and even paralysis. 
Eating pork that is not thoroughly cooked may also lead to trichinosis (infestation with a hairlike nematode worm). When these parasites reach the small intestine, three to five days later many larvae appear which enter the intestine and reach the blood, from which they reach most of the tissues of the body. The larvae move to the muscles and form cysts there, and the patient suffers intense muscle pains. The disease may develop into infection of the cerebral membrane and brain, and infections of the heart muscle, lungs, kidneys and nerves. It may be a fatal disease in rare cases. 
It is well known that there are some diseases that are unique to humans and are nor shared with any other animals except pigs, such as rheumatism and joint pain. Allaah indeed spoke the truth when He said (interpretation of the meaning):  
“He has forbidden you only the Maytah (dead animals), and blood, and the flesh of swine, and that which is slaughtered as a sacrifice for others than Allaah (or has been slaughtered for idols, on which Allaah’s Name has not been mentioned while slaughtering). But if one is forced by necessity without willful disobedience nor transgressing due limits, then there is no sin on him. Truly, Allaah is Oft-Forgiving, Most Merciful”
[al-Baqarah 2:173]
These are some of the harmful effects of eating pork. Perhaps after studying them you will not have any doubts that it is forbidden. We hope that this will be the first step in your being guided towards the true religion. So stop, research, look and think, objectively and fairly, seeking only to find out the truth and follow it. I ask Allaah to guide you to that which is best for you in this world and in the Hereafter. 
But even if we did not know about the harmful effects of eating pork, this would not change our belief that it is haraam in the slightest, or weaken our resolve to abstain from it. You know that when Adam (peace be upon him) was expelled from the Garden, it was because he ate from the tree from which Allaah forbade him to eat. We do not know anything about that tree, and Adam did not need to enquire into the reason why it was forbidden to eat from it. Rather it was sufficient for him, as it is sufficient for us and for every believer, to know that Allaah has forbidden it. 
Look at some of the harmful effects of eating pork; look at the research of the Fourth Annual Conference of Islamic Medicine, Kuwait edition, p. 731 ff; and al-Wiqaayah al-Sihhiyyah fi Daw’ al-Kitaab wa’l-Sunnah by Lu’lu’ah bint Saalih, p. 635 ff. 
But we ask you once again: Isn’t pork forbidden in the Old Testament which forms part of your Holy Book? 
“Do not eat any detestable thing. These are the animals you may eat… The pig is also unclean; although it has a split hoof, it does not chew the cud, you are not to eat their meat or touch their carcasses.”
(Deuteronomy 14:3-8) 
See also Leviticus 11-1-8. 
We do not need to quote evidence that pork is forbidden for the Jews. If you have any doubt then ask people and they will tell you. But what we think we need to draw you attention to is some other things that are also mentioned in your Holy Book, this time in the New Testament which tells you that the rulings of the Torah still apply to you and cannot be changed. Does’t it say in the Bible that the Messiah said: 
“Do not think that I have come to abolish the Law or the Prophets. I have not come to abolish them but to fulfil them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished.”
Matthew 5:17-18? 
With this text, we do not need to look for another ruling on pork in the New Testament, but we will add here another quotation which shows definitively that pork is impure: 
“A large herd of pigs was feeding on the nearby hillside. The demons begged Jesus: ‘Send us among the pigs; allow us to go into them.’ He gave them permission, and the evil spirits came out and went into the pigs.”
Mark 5:11-13 
Perhaps you will say that this is abrogated, and that Peter said such and such and Paul said such and such…? 
This is changing the words of Allaah and abrogating the Torah and the words of the Messiah who confirmed to you that it would abide as long as heaven and earth remain. Can this be abrogated by the words of Paul or Peter? 
Let us assume that this is true and that the prohibition was indeed abrogated, but why are you criticizing this prohibition in Islam when it was prohibited for you at first? 
Thirdly: 
With regard to your saying that if eating it is forbidden, then why did Allaah create pigs? We do not think that you are serious, otherwise we would ask you: why did Allaah create such and such of other things that are harmful or repulsive? Rather we would ask you: why did Allaah create the Shaytaan? 
Is it not the prerogative of the Creator to command His slaves as He will, and to rule them as He will. No one can overturn His ruling or change His words. 
Is it not the duty of the created being, the slave, to say to his Lord, whenever He commands him to do something: “We hear and we obey”? 
You may enjoy its taste and want to eat it, and those around you may enjoy it, but doesn’t Paradise deserve some sacrifice on your part of that which your heart desires?.