I have been working on a world religions guidebook as a very lay level introductory resource for people wanting to learn more about other religions. As I finish chapters I am posting them here for critique and to be a resource. Hopefully you find this helpful as you study Islam.
History & Data
“Islam” is commonly believed to mean peace with God, creation and yourself, but more properly understood by Islamic teaching it means ‘submission’. To submit to the will of Allah is to be Muslim. The term Allah is not a unique name for God in the Muslim faith but simply the Arabic term for God. Arabic Bibles also use Allah for God and Christians in the Middle East often call God Allah.
Muslims view Islam as the first religion, meaning that everyone from Adam to modern Muslims today, are Muslims. With that in mind Muhamad is not seen as the first prophet of Islam but the final prophet of Islam. Muhammad was born in the extremely polytheistic city of Mecca in 560 AD. He quickly became a successful merchant but felt an uneasiness with the religions in Mecca. In search of the true faith he often went into the desert to pray and ask God to reveal himself. One of the days while he was out praying the Angel Gabriel appeared to him telling him that the current religions were all wrong. Over the next 23 years God spoke directly to Muhammad in sayings or Surah’s that were later recorded in the Quran.
Over this time Muhamad spoke as a prophet of the faith and experienced persecution from the leaders in Mecca. As the persecution increased Muslims began to leave Mecca for Medina, Muhammad being the last to leave. There were a number of battles between Muslims and the leaders of Mecca but as Islam grew rapidly the city of Mecca ended up surrendering to Muhammad peacefully when Islam significantly outnumbered Mecca. Islam continued to grow and thrive in Mecca but only three years after returning to Mecca from poison from a Jewish woman who had prepared a meal for him.
Islam grew rapidly across the world arguably much through acts of Jihad and proselytizing. Today Islam is the second largest religion in the world with 1.8 Billion followers and is predicted to surpass Christianity around 2050. The largest populations of Muslims exist in South East Asia in countries like Indonesia, which has the largest Muslim population in the world.
The Quran- This is the central text of the Muslim faith and is believed to be not simply to be the inspired words of God but the literal words of God as given to the prophet Muhammad.
Although, Muslims wish to claim the Quran is uncorrupted, unchanged and includes all of words Muhammad ever said from Allah the Quran in its current form was not finalized till ___ by ____ and much to point out that it excluded certain texts and may not reflect the actual words of as said from Muhammad. 
The Sunnah- a collection of sayings of the prophet Muhammad known as Hadiths and prophetic biography about Muhammad called Sīrah. Which of these Hadiths and Sīrah are viewed as reliable is not agreed upon by Muslims.
The Hadiths- A collection of words, actions and approvals of the Prophet Muhammad. Though the Quran is the central text of the Muslim faith the Hadiths have shaped the Muslim faith more practically and is rightfully viewed as the backbone of the Muslim faith. There is disagreement among Muslims on which collection of Hadiths is most authoritative.
The Inji or Gospel- This is what Muslims would believe is the holy book as given to Jesus. Some Muslims may see The Injil as the entirety of the New Testament, but they would see the New Testament as we have it today as a corrupted and therefore unreliable version of it. Other Muslims would simply say the Injil is the inspiration and revelation that Jesus gave as a prophet but not the New Testament as we have it today.
The Tawrat or Torah/Pentateuch– The revealed text as given to the prophet Moses. This is the Torah/Pentateuch as known to Jews and Christians, but Muslims see at as corrupted and therefore unreliable. This also includes ‘the scrolls of Abraham’ which are the other writings of the Old Testament as well as the Psalms of David.
- Nature of God: Strictly monotheistic or what Muslims call Tawid. Acceptance of even a partner for God, or Trinity, is seen as Shirk or Idolatry. This is the worst sin a person can commit and is an unforgivable sin (Surah 4:48). God is all knowing all powerful, all present, all-knowing, and eternal. He created everything out of nothing.
- Nature of Man: Mankind has a hazed forgetfulness of their goodness and has a leaning toward lowly desires. Everyone is born with an inclination to worship God (Fitrah).
- Fall- The fall is not seen as Adam and Eve taking part in the fruit together. The fall as that event is not central to Islam but mankind is individually sinful, forgetting who they really are and Islam seeks to remind them of their goodness.
- Heaven or Janna- Heaven is a place where all the pleasures of earth and none of the pains earth exist. It is incomprehensibly good.
- Sin- Mankind is not born sinful but does sin and is therefore deserving of punishment for his sin. Muslims believe that there are two angels (Maliakah) assigned to everyone, one records your good deeds and the other your bad deeds.
- Salvation and Judgement- Muslims must submit to the will of Allah and rely upon God for his mercy. Muslims believe that on the day of judgement each person’s good deeds will be weighed out with their bad deeds. Since God alone knows if your good deeds outweigh your bad deeds Muslims as individuals have ultimately no assurance of salvation.
- Creationà End times- Allah created all things out of nothing, and exists outside of creation. Eventually, Allah will destroy all life to bring a final day of judgement, but this will come after a period of tribulation.
- Hell or Jahannam- An eternal afterlife place of punishment for evildoers. Non-Muslims are not necessarily destined to hell because only Allah knows the heart of people and if their good deeds outweigh their bad.
- Unique Theology: Islam believes that God has sent prophets to every nation to preach Islam. There have been 124,000 prophets and the four greatest of these God also gave a holy book to. These prophets are Moses with the Torah, David with the Psalms, Jesus with the Gospel, and Muhammad with the Quran.
Muhammad is the greatest of all of the prophets and Seal of Prophets as the last prophet who is for all time not just a certain age like the prophets before him.
Major Groups or Denominations
Sunni- 88-90% of Muslims.Religious authority is passed on from Muhammad by nomination of Muhammad’s closest friends and followers, Abu Bakr being the first. Election is still how current Caliphs are selected. Religious authority is focused on religious texts, hence Sunni’s refers to other non-Quranic religious texts.
Shi’ite- 10-13% of Muslims. Religious authority is passed on by bloodline, Ali ibn Abi Talib, Muhamad’s son in law and cousin, being the first. Religious authority relies more upon the Iman then religious texts. There has been 12 Iman’s since Muhammad and some believe the 12th is still alive. Ashura is a unique holy day of self-flagellation condemned by Sunni’s.
Sufism– Focuses on the mystical and giving up worldly attachments. Suffism is perhaps better seen as a pursuit of spiritual that transcends any specific religion or sect. In fact, some Sunni’s and Shi’ites practice it. Some Muslims on the other hand would see it as a corrupted Islamic faith.
Traditions and Holidays
Much of the Muslim faith is explained in the Five Pillars of Islam. These Five Pillars are the foundation of Muslim practice.
- Profession of Faith (Shahada)- When one recites the Shahada, “There is no god but Allah, and Muhammad is the messenger of Allah” it is seen as a public confession to be Muslim.
- Prayer five times a day (Salat)- Muslims pray five times a day at specific times faces Mecca. Believers wash before prayer and the prayers are generally set prayers of praise.
- Tithe (Zakat)- Shi’ites generally give 20% of their income while Sunnis generally give 2.5%.
- Fasting during Ramadan (Siyam)- The Holy month of Ramadan is celebrated to mark the day when the Qur’an was first revealed to Muhammad. During this month Muslims fast not only food and liquids but tobacco and sex during the day to follow Siyam.
- Pilgrimage to Mecca (Hajj)- Muslims see Mecca as the center of the world and a holy place since Abraham created a house of worship there. The Ka’aba as it is known was a center of worship of the polytheistic Gods before Muhammad received the Quran. The Ka’aba is believed to be the house of worship made by Abraham and then cleansed when Muhammad came back to Mecca. It is also from here that Muhammad is believed to have had his night journey to Jerusalem and heaven. For the Hajj Muslims that have the financial and bodily ability to visit Mecca and the Ka’aba and go through a week of rituals connected to the significance of the two.
Muslims when asked to summarize the core doctrines of the Islamic faith will often focus on the Six articles of faith listed here. Much of this is already covered above but seeing their summation may be helpful in knowing what Muslims find as central.
- The Oneness of God-
- The Angels of God-
- Divine Revelations- The revelations sent from God through prophets including the Quran, Torah, the gospel, the scrolls of Abraham, and Psalms of David.
- The Prophets of God- Allah has sent messengers to everyone to teach Islam, the greatest of these being Moses, David, Jesus and as the final prophet Muhammad.
- The Resurrection after death and day of judgement
- Preordainment- Allah knows all and nothing is outside his power and knowledge
Bridge Builders & Common Arguments
- Biblical/Quranic Reliability- Be prepared to defend the reliability of the Bible. Muslims are convinced the Bible has been corrupted but are often unfamiliar with how the evidence points to the contrary. On the other side they are shocked to find evidence of the corruption of the Quran. They’ve been told the Quran is the most reliable scriptural text and so it may be helpful to point out the Quran itself claims that previous scriptures cannot be altered (Surah 6:115, 6:34, 10:46)
As mentioned before the Trinity is a beliefs seen as unforgivable to the Muslim. Make sure you can explain the Trinity biblically, reminding them that there is no logical inconsistency to God being a single being in three persons even though we may not be able to comprehend it. Furthermore, make sure they know the Trinity is the Father, Son and Holy Spirit, not Father Son and Mary. Finally make sure they understand Jesus is not God’s physical son, but it speaks to his role in the Trinity, while he is still one in being with God. Calling Jesus the spiritual son of the Father may help them understand this
 “When Ibn Wahb asked Malik B. Anas, about the Uthmanic Codex, he replied, “it has disappeared”. David S. Powers, Muhammad is not the father of your Sons: The Making of the Last Prophet Pg 65-66
Muslims destroyed all of the variants different then the Uthman version, and later even the varients from the Al-Hajjāj version created from the Uthman version. Pg 161