Whats the connection between "Another Brick in the Wall", "Mending Wall", and "Eleanor Rigby"?
All three of the works you mention address the themes of isolation and loneliness, the effect of the barriers we erect to keep us separated from each other. A related theme is conformity, and how it works to perpetuate these barriers.
In "Another Brick in the Wall", the songwriters talk specifically about the barriers, or walls, that parents and teachers build around their children by forcing them to conform to rigid norms. The repeated line "You, yes you, stand still, Laddie" is an adult's reprimand to a child, heard frequently along with other admonitions such as "Wrong, do it again". The harping, negative method of child-rearing serves to create a wall around the child that is imprisoning.
"Eleanor Rigby" depicts people living quiet lives of desperation, struggling within carefully prescribed boundaries to find fulfillment, and never succeeding. The priest and the young woman conform their lives to neatly outlined roles set down for them by society and the church; the priest lives alone, "writing the words of a sermon that no one will hear", and Eleanor Rigby wistfully waits for a man to take her away from her lonely life, only he never does, and she dies "in the church and (is) buried along with her name".
In "Mending Wall", the poet outwardly questions the reason we build so many walls for ourselves, separating us from our true selves and from others. He finds to his bemusement that, what it all comes down to is conformity to tradition. We "move in darkness...(because we) will not go behind (our) father's saying"; it has been said, "Good fences make good neighbors", and because we don't want to question the reason behind the statement, nothing will change.