Messengers: They're the Messangers of God. They're also called 'Apostles'. They recieved Message from their Lord. They're warners against evil - and bringers of Good news to the believers. It's imperative that a Muslim believes in the Messengers...as they're part of the Articles of Faith. Some of the Messengers were given Books - like Abraham, Moses, David, Jesus, Muhammad, and many other more.
Usually, the messangers of God came because of destruction within the Ummah(society). Because of distortion or unbelief within the body of the people - and they were sent to warn people against the evil. Some were denied - actually MOST of them were denied as Messengers, at first. Some of the following are examples:
Prophet Noah's(pbuh) people didn't believe and it was inspired to him that they wouldn't believe. And he was told that his people would not believe and, therefore, would be punished for their unjust. They were drowned. And, Glory Be to Him, God saved the good. Noah and his followers survived and he was told to take a pair of everything that was created, so that the world would go on.
And the Tribe of Aad(Ath,) God send to them their Brother Hud. They disbelieved in him and called his revelations a lie, and God punished them with Tornadoes -- horrible thing was upon them on a normal day. It was "[34:20]Tearing men away as if they were the trunks of palm-trees torn up."
And the Tribe of Thamud, God sent to them their Brother Salih. They disbelieved in him and called his revelations a lie, and God punished them with single loud cry...[54.31] "Surely We sent upon them a single cry, so they were like the dry fragments of trees which the maker of an enclosure collects."
And the People of Lot, God sent them their Brother Lot. They disbelieved in him and called his revelations a lie, and God punished them with a stone-rain that made them crush into nothing..."[54.34] Surely We sent upon them a stonestorm, except Lot's followers; We saved them a little before daybreak."
God also sent Moses and Aaron to the Israelites who were prisoners and slaves for the People of Pharoah. They disbelieved and called their message a lie, and God punished them with a drowning. He(Pharoah) was evil(Pharoah`s People did,) God says "[17.103] So he desired to destroy them out of the earth, but We drowned him and those with him all together;" Now, look back and see what was the end of the unjust. They plan and God planes also; and look who is the best of the planers.
A sad thing that needs to be mentioned is that most of the believers -- took their messengers as lords beside the Lord of the Universe. Jesus was taken as a god beside God. He was a creation himself...while there are people today who pray to him who do things in his name, etc etc etc. Muhammad was taken a god beside God. He was a creation himself who married and ate and lived and died...while there are people today who think he was "better" than all other humans -- and there are people who LITERALLY pray to him! People say his "mosque is haram"(sacred) when God ONLY names one "sacred mosque" in the qur`an.