The message is the lesson or moral, also known as the theme. What is the model millionaire trying teach you? The easiest way to determine this is the ask, what does the author believe? For example, in Finding Nemo, we could say, the author believes that family is an important part of your life as they are your support system. Remove "the author believes that", and what you have left is the important message/theme, which is...
Family is an important part of your life as they are your support system.