Belief in the message of Muhammad comes second only to belief in the one God. Muhammad was born around the year 570 and was orphaned at an early age. He was eventually raised by his uncle, who had religious prominence within the main Quraysh tribe of Mecca but was of modest financial means. At age 25, Muhammad married Khadija, a well-to-do, 40-year-old woman. At age 40, during a retreat in the hills outside Mecca, Muhammad had his first experience of Islam. The angel Gabriel appeared to a fearful Muhammad and informed him that he was God's chosen messenger. Gabriel also communicated to Muhammad the first revelation from God. Terrified and shaken, Muhammad went to his home. His wife became the first person to accept his message and convert to Islam. After receiving a series of additional revelations, Muhammad started preaching the new religion, initially to a small circle of relatives and friends, and then to the general public.

The Meccans first ignored Muhammad, then ridiculed him. As more people accepted Muhammad's call, the Meccans became more aggressive. After failing to sway Muhammad away from the new religion they started to persecute his less prominent followers. When this approach did not work, the opposing Meccans decided to persecute Muhammad himself. By this time, two main tribes from the city of Yathrib, about 300 km (200 mi) north of Mecca, had invited Muhammad to live there. The clan leaders invited Muhammad to Yathrib as an impartial religious authority to arbitrate disputes. In return, the leaders pledged to accept Muhammad as a prophet and thus support the new religion of Islam.

In the year 622, Muhammad immigrated to Yathrib, and the name of the city was changed to Medina, meaning city of the Prophet. This date was designated by later Muslims as the beginning of the Muslim calendar, year one of hegira (Arabic hijra, “immigration”). Only two years after Muhammad's arrival in Medina, the core community of Muslims started to expand. At Medina, in addition to preaching the religious and moral message of Islam, Muhammad organized an Islamic society and served as head of state, diplomat, military leader, and chief legislator for the growing Muslim community. Hostilities soon broke out between the Muslims in Medina and the powerful Meccans. In 630, after a series of military confrontations and diplomatic maneuvers, the Muslims in Medina extended their authority over Mecca, the most important city of Arabia at the time. Before Muhammad died in 632, the whole Arabian Peninsula was united for the first time in its history, under the banner of Islam.

Early accounts of Muhammad contain some stories that describe supernatural events such as his night journey from Mecca to Jerusalem and his subsequent ascent to heaven on the back of a supernatural winged horse. Despite such stories, the primary focus of the biographies, as well as Islamic doctrine in general, is on the humanity of Muhammad. Like all prophets before him, Muhammad was a mortal man, commissioned by God to deliver a message to his people and to humanity. Like other prophets, Muhammad was distinguished from ordinary people by certain powers and faculties. For example, Muslims believe that the distinction of being sinless was granted to Muhammad by God to support his career as a prophet. Thus Muhammad is portrayed in the Qur'an as a person who makes mistakes but who does not sin against God. However, God corrected Muhammad's mistakes or errors in judgment, so that his life serves as an example for future Muslims to follow. This emphasis on Muhammad's humanity serves as a reminder that other humans can reasonably aspire to lead a good life as he did.

As with other prophets and messengers, God supported Muhammad by allowing him to work miracles and thus prove that he was a genuine prophet. The singular miracle of Muhammad and the ultimate proof of the truthfulness of Islam is the Qur'an. In accordance with the words of the scripture itself, Muslims believe that the Qur'an is the timeless word of God, “the like of which no human can produce.” This trait of the scripture, called inimitability (i'jaz), is based on belief in the divine authorship of the Qur'an. Unlike earlier religions, the miracle of Islam is a literary miracle, and Muhammad's other supernatural acts are subordinate to it.

This belief in the unique nature of the Qur'an has led Muslims to devote great intellectual energies to the study of its contents and form. In addition to interpreting the scripture and deriving doctrines and laws from it, many disciplines within Qur'anic studies seek to understand its linguistic and literary qualities as an expression of its divine origins.

The Qur'an is made up of 114 chapters, called suras, which are roughly organized, from the second chapter onward, in order of length, beginning with the longest and ending with the shortest chapters. The first chapter, al-Fatiha (“the Opening”), is a short chapter that is recited during each of the five daily prayers and in many other ritual prayers. All but one chapter begin with the formula "in the name of God, the Merciful Lord of Mercy" (bism Allah al-Rahman al-Rahim). Each chapter is divided into verses called ayat (singular aya, meaning “sign” or “proof”). With few exceptions the verses are randomly organized without a coherent narrative thread. A typical chapter of the Qur'an may address any combination of the following themes: God and creation, prophets and messengers from Adam to Jesus, Muhammad as a preacher and as a ruler, Islam as a faith and as a code of life, disbelief, human responsibility and judgment, and society and law. Later Muslim scholars have argued that the text's timelessness and universality explain the lack of narrative coherence and the randomness of the topics. In other words, the multiple meanings of the Qur'an transcend linear narrative as they transcend any particular historical moment.