The Catholic bible has a book in it called the book of Tobit.  It is about a man who goes blind and has his son work for him.  During his travels, the son meets a woman and marries her.  Throughout the story the angel Raphael helps the man and his son.  Once all is fixed the angel says his goodbyes and goes back to heaven.  The painting shows Raphael saying goodbye and going back to heaven.  There is a pretty good description of everything at the link below.