Jesus talks about the connection of the joy of childbirth to the joy of His return. As a woman goes through the sorrow (pain) of childbirth, when she meets her baby face to face, the feeling turns to joy. For the disciples, as Jesus was taken from the earth, died on the cross, the disciples went through the sorrow (pain) of His death. Soon that sorrow would turn to joy in the resurrection. For us we have the promise of our sorrow (pain) turning to joy as well.