A simple narration from Al Kafi giving a reason on how one should understand the necessity of Prophets.
H 412, Ch. 1, h1 The compiler of this book, Muhammad ibn Ya‘qub al-Kulayni (may Allah grant him blessings) has said that narrated to us Ali ibn Ibrahim from his father from al-‘Abbass ibn ‘Umar al-Faqimi from Hisham ibn al-Hakam from abu ‘Abd Allah, ‘Alayhi al-Salam, the following: “An atheist asked the Imam, ‘Alayhi al-Salam) ‘How do you prove the truthfulness of the prophets and the messengers?’
“The Imam, ‘Alayhi al-Salam, said, ‘It is a fact that we have established with sufficient evidence, proof of the existence of our Creator, the Most Holy, the Most High and Exalted above all creatures. It is a fact that this Creator is All-wise and Most High. His creatures cannot see, touch, associate and directly communicate with Him. It proves that His deputies must be present among His creatures. It is His deputies and ambassadors who speak to people for Him and provide them guidance to protect their interests, to tell them what is beneficial to them and what are the best means of survival and what may cause their destruction. This proves the presence among people of those who convey the commandments of the Creator, Who is All-wise, All-knowing Allah, the Most Holy, the Most High, to people. Such people are the prophets, ‘Alayhi al-Salam, the chosen ones from among His creatures. They are the people of wisdom, disciplined with wisdom and sent to people with the message of wisdom. They are different from other people – although like them in physical form and shape – in their conditions of discipline and their receiving direct support from Allah, the Most Holy, the Most High and All-wise. This also proves their presence among people in all times to ensure the availability of the people with Divine Authority on earth who have the kind of knowledge that would establish their truthfulness and prove them to be of the people who possess the noble quality of justice.’”