In the poem Abou Ben Adhem, the fabled ‘book of gold’ symbolizes its richness and the great value placed on its contents. The angel was writing the names of people who love God. God takes the golden book of mankind and chooses those dear to Him who He will call in the coming year. So, this is not an ordinary book, but a divine one where everyone craves to place his name.
 
In a real world, this is somewhat symbolic of leaving a footprint on the space of time by one’s virtuous deeds. In the poem we see Abou request the angel to write his name on the book of gold as someone who loves his fellow men. And it is not very surprising that the God is happy for his love for men and places his name at the top. People who works for mankind do get a place in people’s heart and memory and in the book of history.