As explained in the first part of the topic, Islam has spread much more quickly compared to other religions all over the world. The traits of Prophet Muhammad (PBUH&HP) were introduced as one of the reasons. Here, the effect of the scientific and social interactions with the rest of the world throughout the Islam's history is discussed. 

 As an introduction, it is good to know that Islam has adopted two types of regulations; confirmed rules and established ones. The Islamic approach regarding the confirmed rules -the regulations which existed before and were conserved or revised if needed- is one of the keys to the development and permanence of Islam. And, this will be the focus of this article.   

Saying Yes to the Good Costumes throughout Islam's History

The Islamic approach to the habits and rules that were common in the pre-Islamic era was that it neither opposed them totally nor accepted them entirely. In some cases, Islam has affirmed and preserved some rules. That was when those rules or customs were not in contradiction to the social order and the living facilities of humans or in case of the righteous customs and traditions that existed before the emergence of Islam; e.g., some of the rules on making contracts. 

However, some of the useful regulations required to be revised and this was accomplished by adding some conditions. On the contrary, some customs and routines were opposed and removed due to the bugs and disadvantages or because they were manipulated or misused for personal benefits; e.g., usury (Riba) [1].

The rules conserved by Islam, such as those about the ownership and property, are called confirmed rules. On the other hand, the rules instituted by the Islamic jurisprudence which never existed before are called established rules [1]. This demonstrates that Islam has always been in constant interaction with the world, and the positive aspects of human societies are considered. Hence, the message of Islam and its framework have not been far from what people are familiar. This consequently has made it easier to accept Islam.

Seeking knowledge; A Way to Spread Islam

Islam has urged everyone to seek knowledge. The first verse of the Quran revealed to Prophet Muhammad (PBUH&HP) enjoined reading which is the key to knowledge: “Read in the Name of your Lord who created” (96:1). Literacy and having knowledge are so important in Islam that Quran equals illiteracy to being in darkness. According to Prophet Muhammad (PBUH&HP), seeking knowledge is obligatory (Wajib) for every Muslim and God loves those who seek knowledge [2].

Learning and seeking knowledge have been emphasized such that Muslims have been encouraged even to travel in order to learn things. Imam Ali (AS) recommended traveling to acquire privilege and named gaining knowledge as one of the achievements of traveling [3]. Prophet Muhammad (PBUH) advised seeking knowledge even if for that purpose one should go to the lands far away [4].

The Holy Quran also addresses the believers as those who are not affected by the wrong behaviors of others since they have been guided. So, the believers can peacefully learn from the positive aspects of others. Another proof of the attention paid to knowledge in Islam is that Muslims used to release the prisoners of wars who taught literacy to a certain number of Muslims. All these emphases and recommendations have urged Muslims to travel to gain knowledge. As a result, Muslims who traveled to other places and countries were practically the messengers of Islam there, which, in consequence, accelerated the spread of Islam.

Continuous interaction with the world During Islam's History 

The actual advances all over the world are the outcomes of the efforts that various nations and civilizations have made in the course of time, among which are the Islamic civilizations [6]. Muslims in different countries, like Spain and Italy, have always been in interaction with other people; therefore, they could transfer the Islamic civilization and culture to others and also receive from them. As an instance, in the battle of the Trench (Khandaq), Salman Farsi proposed to dig a trench around Medina.

This was a tested strategy in Persia, and Prophet Muhammad (PBUH&HP) accepted it. Many of the important Arabic resources and books were translated into European languages, some of which were later on taught and used as references in scientific centers in non-Muslim countries. The bonds between Muslims and Christians through marriage [i] and social relationships were of other means to expose non-Muslims to Islam [7]. All these factors have helped the quick spread of Islam.

From what has been discussed, we can see that the Islamic approach of making regulations under the form of confirmed rules, the encouragement to obtain knowledge and literacy, and cultural exchanges with the rest of the world played significant roles in attracting many savants and people to the religion of Islam.    

Notes:
[i] This kind of marriage named Interreligious marriage is permitted in Islam under the certain conditions. 

References:

1. spreading Islam
2. “Misbah al-Shariah”, p. 13.
3. M. Nuri, “Mustadrak al Wasail”, vol. 18, p. 115.
4. “Misbah al-Shariah”.
5. “Ghurar al-Hikam wa Durar al-Kalim”, p. 46, T. 188.
6. history of Islam
7. A. Velayati, “Dynamism of Islamic and Iranian Culture and Civilization”, vol. 1. 

One of the main differences between Islamic and non-Islamic lifestyle is manifested in the eating habits. Not eating pork and not drinking wine are two of these practices which are indeed evident in the life of a Muslim.  This article will briefly analyze some of the reasons why Muslims do not consume pork.  

However, it is important to keep in mind that the central philosophy behind all religious rules including Islamic rules and regulations is only known by the All-Wise and All-Knowing God who is the Creator of the whole universe and all the creatures.

Religious Reasons:

Pork is forbidden in different Divine religions. For instance, the Bible says about pork: "And the swine ...  he is unclean to you. Of the flesh shall ye not eat, and their carcass shall ye not touch; they are unclean to you." (Leviticus, 11:7-8). The same command is repeated in Deuteronomy, 14:8.

Christians often depict Satan in religious anecdotes in the form of a pig. The Gospel of Barnabas mentions that Pig is Satan personified and that the pig’s body has the spirit of Satan. The present Bible among the Christians (Matthew 8-32 Marks 5-13, Luke 8: 28-39) describes how Jesus thrust the soul of Satan inside the herd of swine and sent them towards the river [1].

In Islam, there are two primary sources for understanding the orders of Allah: the Quran and the Sunnah [2].  Both the Holy Quran and Sunnah have equal status as far as the obligatory orders (wajibat) are concerned. If one wajib is mentioned in Sunnah only, it has the same weight as one said in the holy Quran only [3] and vice versa.  Both sources mention that eating pork is forbidden.

Allah has announced that eating pork is forbidden in several verses of the Holy Quran:

“You are prohibited carrion, blood, the flesh of swine …” (5:3).

The unclean nature of swine flesh is stated in the following verse:

“Say, ‘I do not find in what has been revealed to me that anyone be forbidden to eat anything except carrion or spilled blood, or the flesh of swine —for that is indeed unclean— or an impiety offered to other than Allah.’ …” (6:145)

The same concept is declared in the verses (2:173) and (16:115).

Imam Reza (AS) mentions regarding the prohibition of pork, “The Almighty Allah has prohibited (made Haram) Pork because it is a horrible and dreadful animal that Allah has created for men to derive lessons from. People should also refrain from sensuality and shameless deeds that cause such a terrible appearance. And that they fear from being transformed into pigs by Almighty Allah. (In the description of past nations it is mentioned that people who committed sexual promiscuity are changed into pigs in the Intermediate world (Barzakh) [i], and they shall be raised as pigs in the Judgment Day (Qiyamat)).

Also, pigs were allowed to exist so that they are a reminder of the metamorphosis (Maskh) [ii] of previous nations into pigs. The second reason for prohibiting pork is that the staple diet of pigs consists of extremely impure (Najis) and filthy things, and its blood contains innumerable harmful germs.” [4]

Imam Sadiq (AS) said,“The Almighty Allah metamorphosed many nations into animals. Among them are pigs, monkeys, and bears, etc. After this these animals were prohibited from being eaten so that people derive lessons from them and do not consider the sin minor.”[5]

Pork is very harmful to the body but we mention below only some of its harmful effects.

Scientific Reasons:

The present-day science of parasitology has proven some serious diseases in human beings caused by the bacteria and germs found in pork.  Pork is the main carrier of many germs and parasites such as Faciolopsis buski, Paragonimus, Clonorchis sinesis, Erysipelothrix rhusiophathiae [6]. Moreover, Dr. Joseph Mercola has cited the following diseases caused by pork: Porcine Reproductive and Respiratory Syndrome (PRRS), the Nipah Virus, Porcine Endogenous Retrovirus (PERV) and Menangle Virus [7].

On the whole, the pig is the cause of many serious and fatal diseases, among them, dysentery, trichinosis, tapeworm, roundworm, hookworm, jaundice, pneumonia, suffocation, intestinal obstruction, acute pancreatitis, enlargement of liver, diarrhea, emaciation, stone formation in liver, cancer, anemia, high fever, hindrance of growth development in children, typhoid, lameness, heart trouble, abortion, sterility, and sudden death [8].

It is important to note that despite hard efforts in medical science, many of the pig parasites cannot be eliminated by antibiotics, drugs or vaccines.

Some people assert that by present day means it is possible to eliminate all these parasites and make pork devoid of them, but even upon the supposition that use of sanitary equipment or cooking of meat at high temperatures eliminates all the parasites, nevertheless the harms associated with pork cannot be denied for according to the incontrovertible law, the meat of every animal bears the traits of that animal and, by means of the glands and the hormones secreted by them, influences the conduct of those who consume it.

Thus, consuming pork may transfer the attributes of sexual depravity and indifference towards the affairs of the womenfolk of the family - the most blatant traits of the male members of this species - into the person who consumes it.  And perhaps, one of the reasons for the excessive sexual profligacy dominant in the West could be consumption of the meat of this sordid animal [9].

So since the scope of science and the knowledge of human beings are limited, there might be other harms still undiscovered. However, even if human beings find some way of eliminating all the physical and spiritual harms of something, it does not mean that the forbidden (Haram) law of God becomes permissible (Halal). As mentioned at the beginning of the article, we must submit to the will of God as the Creator of the whole world and the Only One who truly knows about what is good and bad for the creatures and why.

Notes:

[i] The stage between this world and the hereafter

[ii] In Arabic, Maskh means for something to change form to an uglier one. In the Quran and Islamic tradition, this term refers to a specific divine punishment which was sent upon the wrongdoers and wrongdoing nations in the past (of course not all wrongdoers, but those who committed certain wrong acts) which can be called metamorphosis. For more information, please refer to http://www.islamquest.net/en/archive/question/fa614

References:

1. eating in Islam
2. Sunnah means the sayings, actions and silent approval of the Holy Prophet and the Holy Imams (PBUT).
3. islamic laws
4. Uyun al-Akhbar ar-Riďa & Wasa’il al-Shia, ch.1 
5. food in Islam
6. eating pork in Islam
7. all about pork meat