Islam is split into two main branches: Sunni & Shia. They each interpret Muhammad's wishes for his next successor differently.
Sunni Muslims believe that Abu Bakr was rightfully the successor of Muhammad, as he was elected by the community.
Caliph: The title given to the leader of the Muslims after the death of Muhammad.
Sunni Muslims are guided by the Caliphate.
Sunni Muslims believe in authority of the Qur'an & the Hadiths.
The six articles of faith in Sunni Islam:
Tawhid
Angels
Judgement day
Prophets
Allah's will
Authority sources
Tawhid is the 'oneness of Allah'. Both Sunni & Shia believe in Tawhid, however Shia include angels as part of Allah.
Angels: Immortal beings which follow Allah's will rather than their own.
Judgement day: The idea that Allah will judge every human & place them in a level of Jannah (Heaven) or Jahannam (Hell) according to their life on Earth.
Prophets of Islam: Jesus, Moses, Muhammad, etc.
Allah's will: An article of faith stating that Allah is supreme & omniscient over all living things.
Authority sources in Islam: Psalms of David, Torah, Gospels, Scrolls of Ibrahim & the Quran.
The Quran is the most important holy book of Islam, as they believe it is the unchanged word of Allah.
Shia Muslims believe that Ali was intended to be Muhammad's successor.
Shia Muslims believe in the imamate- a leader chosen by a previous imam, who interprets the Quran correctly.
Shia Muslims practice annual mourning for Husayn (Muhammad's grandson) by punishing themselves.
The five roots of Shia Islam:
Tawhid
Justice of Allah
Prophethood
Judgement day
Imamate
Justice of Allah: A root of Shia Islam stating that Allah is just, wise & omniscient. Similar to the article of faith 'supremacy of Allah'.
Both Sunni & Shia Muslims believe in Judgement day.
Imamate: Protectors of the Islamic faith (in Shia Islam) who ensure that teachings do not become corrupt.
The first 11 Imams led the Islamic Shia community & the 12th is said to be in hiding.
"He who is the all-knowing, the all-powerful able to do anything" - Quran, on the topic of Allah's omnipotence.
Examples of Allah's omnipotence include: the 7 days of creation, control over angel messengers & Jannah and Jahannam.
"He is Allah, one, Allah the eternal refuge. He neither begets nor is born.Nor is there to him any equivalent" - Quran, on the topic of Tawhid.
Tawhid impacts Muslims, as they will not worship anything other than Allah.
Tawhid differs from Christianity, the trinity would break the idea of 'oneness'.
Immanence: The idea that God is present on the Earth & can contact or be contacted by humans.
"We are nearer to man than his jugular vein" - Quran, on the topic of immanence.
"And he is with you wherever you may be" - Quran, on the topic of immanence.
Immanence of Allah can be proved through:
Miracles, humanity & nature existing
Prophethood
Angels visiting Earth
Transcendence: The idea that Allah is beyond human understanding, & so he can control the world but isn't affected by it.
"Nothing is impossible with God" - The Bible, on the topic of Immanence & transcendence.
"No vision can grasp him... He is above all comprehension" - Quran, on the topic of transcendence.
Since Allah is outside of time & beyond human understanding, he cannot be part of the Earth, so must be transcendent.
Moral evil: Human caused suffering, believed to be a part of Allah's will, as all shall become fair on judgement day.
If Allah is omnipotent, he should have the ability to give all humans the same opportunities & fulfilling lives. All beings should be loved & not tormented or tested.
Allah's omniscience & omnipotence mean that he has the ability to fix unjust issues, yet chooses not to.
Some Muslims may argue that suffering is simply a test to determine a place in the Afterlife. Prophets were sent to guide humanity, & so it is not Allah's fault if humanity disobeys.
"Be a steadfastwitness for Allah in equity & let not hatred of any people seduce you that you deal not justly" - Quran
On Earth, Muslims cannot always witness justice being served as they do not understand how Allah acts. They must instead wait for Judgement day to be placed in Jannah or Jahannam.