Why did the pope say gender is a property of essence?

In his 2012 Christmas address , Pope Benedict XVI said: > According to the biblical creation account, being created by God as > male and female pertains to the **essence** of the human creature. The use of the word "essence" puzzles me here. I wonder whether gender is a property of essence or existence. Does gender still exist in Heaven? Isn't gender a property of the body rather than an attribute of each being? If so, gender is tied to existence. What is official Catholic teaching on this?