I believe that adoption is a fitting illustration of his relationship with us because it singnifies his love for mankind. When potential parents go to an adoption agency to adopt they specifically choose the child they want. God specifically chose mankind in his mind & redeemed us with his blood. To know that the creater of all the universe picked you out is fantastic. That should be enough to encourage anybody. This is the gospel that needs to be preached. That God so loved the world, that he gave his only begotten son, & whosever believith in him should not perish, but have everlasting life!