The song has no meaning the same as most songs. This one particularly was aimed at the start of lessons in the English Schools Curriculum that had a provision for analysing the lyrics of songs including Beatles songs. Lennon, realising this to be a nonsense due to it being a subjective exercise rather than objectively asking the original composer, set about constructing a song that would be impossible to analyse in such a way. It didn't quite work as I was set an exercise at school to analyse U2's Running to Stand Still over 20 yers later.