He wanted people to stop worshiping idols and to follow only Allah. He taught that the other two Semitic religions had also been revelations from God, but that over time people had distorted and changed the message, and that his job was to set the teaching straight.

As was common in his time, Muhammad didn’t read or write, but preached by giving sermons wherever he went. Much later, after his death, his followers decided to compile his words into a book. This book is the Koran (sometimes spelled "Quran"), which is considered by Muslims to be literally the word of God, as received by Muhammad. Because the Koran was originally written in Arabic, many Muslims feel strongly against it being translated into any other language, as translation always carries a risk of changing the meaning. Throughout the centuries, Muslims have memorized huge portions of the Koran, reciting them during prayer. Some memorize the whole thing, and take great pleasure in reciting it at gatherings of other believers, because it is felt to be so beautiful.

Another book that is special to Muslims is called the Hadith. The Hadith is full of stories of the life and teachings of Muhammad as told by those who actually knew him.

This beginning quote from the Koran shows the Islamic belief in Allah as compassionate and loving, and also the belief in Judgment Day.

Praise be to Allah, Lord of the Creation,

The Compassionate, the Merciful,

King of Judgment-day!

You alone we worship, and to You alone we pray for help.

Guide us to the straight path

The path of those whom You have favored,

Not of those who have incurred Your wrath,

Nor of those who have gone astray.