The theme of this song is certainly not subtle: it's about lonely people. But stating it thus doesn't do justice to what the Beatles were really saying. A closer inspection reveals that this song examines why the lonely people are lonely.
The song has two characters, Eleanor Rigby and Father McKenzie. These two are connected by the church, in this case the actual church that Father McKenzie preaches at and Eleanor Rigby cleans. She is -- and this is not apparent immediately -- a custodian in this church. How do we know that she's the custodian? Well, she picks up rice after weddings...that's a clue. And she died in the church...that's another clue.
At this point, it's good to ask students, if Eleanor Rigby is a custodian, why did the Beatles choose the post-wedding cleanup as the one image showing this? Students usually will quickly come to realize that this image reflects the "dream" she lives in: she wants to marry.
Here's where I tell my classes, artists never choose details indiscriminately. Every description is a clue, a symbol, a piece of the jigsaw puzzle. That is, often, the difference between good art and mediocre art. Mediocre artists often cannot tell you why they chose this detail or that shade of coloring; it just felt right. Great artists know why they do what they do.
Back to the song. Eleanor's dream is further developed in the strange line "wearing a face that she keeps in a jar by the door." This is a great line to have students puzzle over. Eventually, with a little nudging, they'll see that this face is probably the face that she puts on to look beautiful, the jar being the makeup jar from which the face comes. She waits each night by her door, waiting...