The meaning of Iman is that what ever Allah سبحانه و تعالى (may he be glorified and exalted) has conveyed to us through the Prophet صلى الله عليه وسلم (may Allah honor him and grant him peace), to accept it to be true and believe it by heart is called Iman.
Allah سبحانه و تعالى has mentioned all the matters of Iman in the Qur'an and Hadith (traditions) and teachings of the Prophet صلى الله عليه وسلم.
There are many matters of Iman, amongst them some of the most important matters of Iman are as follow:-
1. Belief In Allah
Belief in Allah سبحانه و تعالى means, Allah سبحانه و تعالى is such a being that he is in existence by himself, no one has created him. Allah سبحانه و تعالى is from ever and will be forever (eternal), he has all good attributes, and he has no faults or defects.
Allah سبحانه و تعالى is the creator of the whole universe and what ever is in the universe.
Allah سبحانه و تعالى is the only one worthy of worship; the meaning of worship is the utmost honour, respect, and glorification. All the acts of Ibadah such as Salah - Prayer, Zakat - Charity, Sawm - Fasting, and Hajj - Pilgrimage are means of worship.
2. Belief In The Angels
Allah سبحانه و تعالى has created the angels from noor - light they are always obedient to Allah سبحانه و تعالى, they never disobey Allah سبحانه و تعالى.
Allah سبحانه و تعالى organizes the whole matter of the universe through the angels e.g. sunrise, sunset, blowing the wind, rain and removal of the soul etc.
The angels cannot be described as males and females; no one knows their number besides Allah سبحانه و تعالى.
3. Belief In The Books Of Allah
Allah سبحانه و تعالى sent down many small and big books through the prophets, which contain commands and guidance for the people, the books inform the people of right and wrong matters, and beneficial and harmful matters concerning this world and the hereafter.
There are four famous books: -
1) Tourat revealed to Prophet Musa عليه السلام (peace be upon him)
2) Zabour revealed to Prophet Dawood عليه السلام
3) Injeel revealed to Prophet Isa عليه السلام
4) The Qur'an revealed to Prophet Muhammad صلى الله عليه وسلم
The people have changed and altered the first three books. Only the Qur'an is in it's original form, and will be until the day of judgement, because Allah سبحانه و تعالى has taken the guarantee of protecting the Qur'an.
It is necessary to believe that Allah سبحانه و تعالى revealed these three books also, but after the Prophet Muhammad صلى الله عليه وسلم it is only permissible to act and practice according to the guidance of the Qur'an.
Only acting and practicing according to the Qur'an will enable the person to be counted as a believer, hence will be be saved from hell, and be put into Paradise.
Now if any person practices according to any other book besides the Qur'an. then that is not sufficient for his salvation in the hereafter, and one will not be counted as a believer but will be counted as a non-believer.
4. Belief In The Prophets
Allah سبحانه و تعالى chose from amongst mankind many people who were pious, obedient to Allah سبحانه و تعالى, of highest intelligence, understanding and of highest morals and character.
Allah سبحانه و تعالى revealed his messages and commands to these people sometimes through the angels and sometimes Allah سبحانه و تعالى revealed the messages and commands directly on to their heart.
These people are called Messengers and Prophets. They are human beings and they have all the needs and characteristics of human beings eg. Eating, sleeping, marriage, transactions, happiness, sorrow, etc.
They inform people of the commands and messages of Allah سبحانه و تعالى verbally by reciting and explaining the verses which have been revealed to them, and they also teach the people how to practice these commands by acting and carrying out these commands practically themselves.
They guide people in every aspect of life in such a way, which is beneficial for the people in this world and the means of acquiring the pleasure of Allah سبحانه و تعالى and Paradise in the hereafter.
They guide people in the acts of worship, transaction, character and social behavior in a way, which disciplines the person and creates unity and harmony amongst the people and takes away injustice and oppression from the community.
Allah سبحانه و تعالى choose many people for prophet hood. Some of the famous Prophets are:
Hadrat Adam عليه السلام
Hadrat Nooh عليه السلام
Hadrat Ibrahim عليه السلام
Hadrat Musa عليه السلام
Hadrat Dawood عليه السلام
Hadrat Isa عليه السلام
Prophet Muhammad صلى الله عليه وسلم.
Prophet Muhammad صلى الله عليه وسلم is the last Prophet. No new Prophet will come after Prophet Muhammad صلى الله عليه وسلم.
Hadrat Isa عليه السلام will descend from the skies onto the earth before the day of resurrection and he will govern and guide the people according to the Islamic law of Prophet Muhammad صلى الله عليه وسلم, ie. He will act and govern as a deputy of Prophet Muhammad صلى الله عليه وسلم.
5. Belief In The Hereafter
Allah سبحانه و تعالى has created this world for a certain period of time. After the completion of that period the world will be destroyed. All the human living creatures will die.
This destruction of the world is called Qiyamat (Judgement day). After that
Allah سبحانه و تعالى will create a new system.
All the human beings and living creatures will be brought to life and all of them will be gathered on one plain ground and everyone will have to account for their deeds, which they carried out in their worldly life.
The deeds will be weighed in the scales. The righteous deeds will be put on the right side of the scales. The evil deeds will be put on the left side of the scales.
If the scale of the righteous deeds is heavier than that person will be entered into Paradise, and if the evil deeds are heavier then that person will be entered into Hell, unless Allah سبحانه و تعالى forgives that person without punishment.
The person who dies as a non-believer or a polytheist he will stay in Hell forever and he will never be forgiven.
When a person dies as a believer and his virtues are more than his sins, he will enter into Paradise without any punishment by the mercy of Allah سبحانه و تعالى.
If a person dies as a believer but his sins are more than his virtues then his fate is in Allah سبحانه و تعالى wish.
If Allah سبحانه و تعالى wishes then he will be punished first. Then after the completion of his punishment he will be taken out of Hell and entered into Paradise or if Allah سبحانه و تعالى wishes then Allah سبحانه و تعالى will forgive him without any punishment and enter him into Paradise.
In the hereafter people will live forever. Once the believers enter Paradise they will never be taken out of Paradise.
The last believer who will enter into Paradise, will be given the Paradise which will be ten times the size of this world.
6. Belief In Taqdir
The meaning of Taqdir is that what ever has happened or what ever is happening or what ever will happen. Everything happens according to the way Allah سبحانه و تعالى has planned. Allah سبحانه و تعالى knows about it before it is happening. This is the meaning of Taqdir.
Eg. Allah سبحانه و تعالى has planned and knows when a person is going to be born, how long he will live, what type of acts he is going to carry out (ie. Good or bad), how much sustenance his is going to receive and whether he is going to die as a believer or a non-believer.
By this pre-planning of Allah سبحانه و تعالى a person does not become helpless because Allah سبحانه و تعالى has blessed every person with a will power, intention, and strength which allows him to carry out any act of obedience and virtue or any act of disobedience and sin. By his free will and control.
Thus with his free will and control if he carries out an act of virtue he becomes eligible for reward and Paradise, and with his free will and control when he carries out an act of sin he becomes entitled to punishment and Hell.
For a person to be a believer it is necessary to accept and believe by heart everything, which Allah سبحانه و تعالى has revealed to us through Muhammad صلى الله عليه وسلمin the Qur'an and in the teachings of Muhammad صلى الله عليه وسلم.
The above mentioned are only some of the very basic and fundamental beliefs of Islam. There are many more matters of belief eg. to believe that five times salah in a day is a compulsory act of Islam. The fast of the month of Ramadhan, the paying of zakat and the performance of Hajj are compulsory acts of deen and Iman.
The Prophet Muhammad صلى الله عليه وسلم said,
“The superstructure of Islam is raised on five (pillars) : testifying that there is no God (none truly to be worshiped) but Allah, and that Mohammad is the messenger of Allah, performing the prayer, paying the Zakah (poor-due), fasting the month of Ramadan, and performing Hajj.” (Bukhari & Muslim)
Shahada - The testimony of faith
The first part is to testify: "that there is no God but Allah"
Which means that you believe that there isn't any other God except the one and only true God, 'Allah'
The second part is to testify: "that Muhammad (peace be upon him) is his servant and messenger."
أشهد أن لا إله إلاَّ الله و أشهد أن محمد رسول الله
“I bear witness that there is no God (none truly to be worshiped) but, Allah, and I bear witness that Mohammad is the messenger of Allah."
لا إله إلا الله محمد رسول الله
"There is no god but Allah, Muhammad is the messenger of Allah."