I guess you didn't click on the link to the other post of mine. So here it is ....
Here's more detail on
the need for Revelation
So here is the Islamic version as to what this Revelation is. Revelations are God's word sent to Prophets of God through Angel Gabriel as a guidance to mankind. According to Islam, Revelations by God has been conveyed to humanity throughout the history of mankind via God's messengers - all the prophets starting from Prophet Adam(PBUH) and then continuing with many other including Noah(PBUH), Abraham(PBUH), Moses(PBUH), Jesus(PBUH) and finally ending with Prophet Muhammad(PBUH).
"Say, [O believers], "We have believed in Allah and what has been revealed to us and what has been revealed to Abraham and Ishmael and Isaac and Jacob and the Descendants and what was given to Moses and Jesus and what was given to the prophets from their Lord. We make no distinction between any of them, and we are Muslims [in submission] to Him." (Al Qur'an 2:136)
However, as time went by every time after the prophets left, mankind went astray from the teachings and worship of God to 'worshiping their desires'. Some of it could be due to people becoming rebellious and arrogant or some of it could be because people started coming up with their own ideas as to how to worship God. And generations later there was no way to get back to the original and the same True message of God that all the messengers brought due to lack of preservation of the message. And then God sent the last and final messenger, Prophet Muhammad(pbuh) with the same message confirming the previous messages. And His followers made very meticulous effort (with God's help obviously) to preserve the message for any generations to come. Just some related verses so you know what it says :
"Muhammad is not the father of any of your men, but (he is) the Messenger of Allah, and the Seal of the Prophets: and Allah has full knowledge of all things." (Al Qur'an 33:40)
"We have, without doubt, sent down the Message; and We will assuredly guard it (from corruption). We did send messengers before thee among the religious sects of old: But never came a messenger to them but they mocked him." (Al Qur'an 15:9-11)