Why does Scrooge need to beware mankind?

This was the warning issued to him by the Ghost of Jacob Marley. In both their lives Scrooge and Marley cared little for the plight of people around them; they saw only business and money. However, Marley's warning tells Scrooge that this is wrong and that he (Scrooge) should be aware of such issues in the world around him and seek to care for the plight and suffering of others, and seek to find where he can help make changes.