When it comes to sermon writing, generally there are two problems. Some preachers love the research stage but hate the writing, and they start writing too late. Others don't like doing research, so they move way too fast to the writing part.
As a preacher who is fully human, and clearly not divine, I can't speak as Jesus did. But I do seek to speak truth that carries weight and authority. All of us who preach the gospel aspire to speak under the authority of Jesus.