The angel who surprised some shepherds outside of Bethlehem brought them good news. They were told that a baby had been born who would be a savior and that they were being invited to go and see him. I suspect the shepherds thought they deserved some good news. Things were not going very well. They were living in a nation that had been conquered by Rome and the recent requirement that everyone be registered in their hometown was for the good of Rome, not for them. It is likely that the kind of savior they were looking for was one who would save them from their Roman oppressors.
The shepherds answered the invitation and went to see this baby who was going to be a savior and told Mary what the angel had told them. Mary pondered this in her heart. She knew something the shepherds did not. She knew that this baby, who the angel said would be the Messiah and Savior, was not an ordinary child. He had been conceived miraculously by the Holy Spirit. She also knew that an angel had told Joseph that they should name the baby Jesus because he would save his people from their sins. That was a deeper good news than the shepherds probably understood.
When we think of good news in medicine it commonly means that a new more effective treatment has been developed or possibly that a disease that previously had no effective treatment can now be cured. Those things are good news, but however many new treatments are developed, we still all die.
The good news of Christmas gets at something deeper. The Bible helps us understand that the reason that the diseases and death that medicine battles exist in this world is because we and the world we live in are broken by sin. No matter how many new treatments we develop, medicine cannot address the underlying problem. The angel told the shepherds about the ultimate cure. A savior had been born who could reverse the effects of sin and death and save us from our sin. He could bring us eternal life. He did that by going to the cross and showed his victory over sin and death by his resurrection. That is good news.