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.
Matthew 13:54-58
"And when he was come into his own country, he taught them in their synagogue, insomuch that they were astonished, and said, Whence hath this man this wisdom, and these mighty works? Is not this the carpenter’s son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas? And his sisters, are they not all with us? Whence then hath this man all these things? And they were offended in him. But Jesus said unto them, A prophet is not without honour, save in his own country, and in his own house. And he did not many mighty works there because of their unbelief"