Jesus brought the Gospel (Injeel), by the permission of God, but it was changed by evil people, who made Jesus god or son of God, that's why it was needed another Revelation to undo the previous corruption. Prophet Muhammad was chosen to be the Messenger of the Quran (The word of God, brought down by Gabriel/Jibril). Muhammad was also named as the seal of prophets, (meaning the last one, but not the greatest one as some sects like sunni or shia present it). It means the Quran will be preserved until the Day of Judgement and it doesn't need more Revelations or Messengers. Isn't it obvious. [15 : 9] Indeed it is We who have sent down the Qur'an and indeed, We will be it's guardian.
The Quran was given to Mohammed by Gabrielle when Muhammad died many qurans were collected and piled Together and destroyed an it was Pieaced together by one or group of men.who knows what was lost. remember the message Was giving to Mohammed Not the people who collected it and compiled it together for people to remember.
Wdym the Quran was given?Did you think Allah just sent a book from heaven to Prophet Muhammad Sallallahu Alaihi Wasallam? Rather it was revealed on a span of 23 years with different chapters and verses simultaneously. The Prophet Sallallahu Alaihi Wasallam would memorise it and tell his companions to do same . And the scribes would write it down on personally. So yeah it wasn't in book form originally as it was revealed over a span of 23 years. After Prophet Sallallahu Alaihi Wasallam's Death Abu Bakr Radiallahu anhuma told all the scribes and hafiz(memories) to form a council to preserve the Quran. And so it was cross verified by both reciting and writing and finally the Quran was compiled in a book .That's it . The Quran is the single greatest preserved historical document in the history of existence . Werher you accept or deny the truth remains unchanged.