Allah wants to guide people and help them attain salvation. As a just God, the God of Islam must therefore send Prophets to guide mankind to the proper path. 

The word prophet in the English language is not always synonymous with the Islamic term nabī. Nabī is someone who receives wahī which is a special kind of direct revelation that a person receives through the medium of the Archangel Gabriel.  

A rasūl is a higher ranking nabī who receives a whole new system of laws. A basic nabī may receive a specific law, but he does not receive a system of laws. 

According to Islam, the purpose of Prophethood is to guide mankind towards salvation in this world and in the Hereafter. Prophets bring the blueprint on how to live the proper spiritual, moral and material life. They not only teach the blueprint, but they also act as role models for us to follow. 

The Prophet Muhammad was both a nabī and a rasūl. As the final Prophet of God, he was the universal messenger for all of mankind. Among all Prophets, he was the most perfect in knowledge and in character. As the final and universal Prophet, his message is meant for all of mankind in all places and all times.  

As a role model, the Prophet's actions are known through his Sunnah (tradition). His sunnah is recorded in a oral tradition called the hadith, which are sayings of, or about the Prophet (i.e what he did). The Prophet’s main miracle was his own message in the form of the Qur’an, the Divine Scripture of Islam even though he had other miracles as well. 

The correct interpretation of the Qur'an and the Prophet's teachings had to be protected after the Messenger of Allah's death. For this reason, God chose Imāms from the Ahl al-Bayt, or the Holy Household of the Prophet (s), to guard their correct interpretation.