In ancient Arabia, poetry was considered a powerful supernatural art. Poets were called Sha'irs and were feared and revered as magicians. The Sha'ir would travel into the wilderness where, Arabs believed, they associated with desert demons: Djinn (genies) and Shayton (satans). These desert demons whispered verses into the ears of the Sha'ir. When the poets returned to town they recited these verses like supernatural incantations.
The verses of the poet could be used to bless or to curse. They could elect leaders and start wars. In fact, before a battle each army would send out their poets to ridicule the enemy. Sometimes the poets of one side were so successful that they won the war without the warriors ever fighting.
Poetry was also used to praise the gods. Each of the many ancient Arabic gods had a group of Sha'ir who would compose verses in their honor. Based on the skill of these poets a god's power and influence might grow or wane.
Muhammad was not a Sha'ir (the Quran repeats this several times). He was a shepherd and caravan leader. But like the Sha'ir, he spent time in the wilderness, meditating in his cave. And like the Sha'ir he heard a voice in his ear. It was the voice of the Angel Gabriel who asked him to recite the Quran - a long multipart sacred epic poem to the God, Allah.
Three times Muhammad refused. He said that he was not able to recite the Quran because he was illiterate (he could not read or write). But the Angel insisted and finally Muhammad agreed. For the rest of his life Muhammad heard the Angel's voice reciting to him the Quran. He described the voice as sounding like the buzzing of bees.
Muhammad memorized each verse of the Quran that the Angel told him and then recited it to the people of Mecca. Upon hearing the Quran, many Arabs immediately turned from their tribal gods to only worship Allah. It was the most tremendously powerful sacred poetry they had ever heard. Meccans hearing the Quran for the first time would cry, fall to the ground, and sometimes shake violently.
The Quran speaks about many subjects. Sometimes it gives laws, like the Commandments. Sometimes it is pure poetry. Most of the Quran is a telling of the stories of the Prophets: Adam, Abraham and Sarah, Isaac and Ishmael, Jacob, Joseph and Zulayka, Moses, Mary, John and Jesus. The Quran refers to itself as an Arabic edition of the Bible.
Reciting the Quran is still the most sacred act in Islam. Even more important then the meaning is the sound of the Quran, because it is the exact syllables that God spoke through the Angel Gabriel. Hearing or making these sounds brings the Muslim into a rapturous union with God. It is like speaking directly with God.