The first book in the New Testament is the Gospel of Matthew. It's author was a tax collector until he was called by Jesus to be one of His 12 disciples.
Matthew's Gospel was written about 20-30 years after Jesus had ascended to heaven. During that time the good news had spread throughout the Roman Empire, but Christians were starting to be persecuted. The aim of Matthew's Gospel was to strengthen the faith of Jesus' followers during these hard times, and also to give them a tool to help them spread their faith to others.
"Again, the kingdom of heaven is like unto a net, that was cast into the sea, and gathered of every kind: which, when it was full, they drew to shore, and sat down, and gathered the good into vessels, but cast the bad away. So shall it be at the end of the world: the angels shall come forth, and sever the wicked from among the just, and shall cast them into the furnace of fire: there shall be wailing and gnashing of teeth."
There is debate about the meaning of Jesus' words. Some believe that the furnace represents the eternal torment of Hell, whilst others say that the furnace represents the destruction of the wicked. Either way, the wicked will not see the Kingdom of God