While we have to "Imagine" , we also have to "Let It Be". Much more popular than other songs of the Beatles, this song says "Mother Mary comes to me Speaking words of wisdom". One could argue, that songs popularity comes from its religious connotation, but could also be due to its "wisdom" coming from a mother(Paul's). Another, interpretation i have heard is "Mary" being a herb!! This also makes sense, as "And in my hour of darkness she is standing right in front of me".
This song offers a solution, "And when the broken hearted people living in the world agree There will be an answer". So we can wait for the "broken hearted" to agree and "Let it be".