I realise this is an extremely hard song to listen to, for all sorts of people and for all sorts of reasons. I'm not including it here because it entertains (it clearly doesn't) but because of its cathartic honesty.
Mother was the opening track to the first post-beatles album by John Lennon (John Lennon/Plastic Ono Band). Both John and Yoko had been exposed to Arthur Janov's primal therapy and the natural outcome was music that reflected their experiences (Yoko's response was the twin album, Yoko Ono/Plastic Ono Band).
The opening tolling of bells has been seen as signalling the passing of the Beatles-era for Lennon, a topic he addresses on the song God later on the album. Whether intentional or not, the effect is palpable. But even more they signal the sense of loss and rejection that the song goes on to handle, as indeed does the whole album in various ways.
A rewarding listen, but not an easy one.