Impossible question - but possibly one of these:-
The eponymous "All you need is Love"
"Time is short and the days are sweet" From Dylan's Dark Eyes
"What makes you go abroad, fighting with strangers?" from Our Captain Cried All Hands.
"Amoebas are very small" Mike Heron - A Very Cellular Song
"There is a crack in everything, that's where the light gets in" might just win by a nose (Anthem - Leonard Cohen)
But I'll probably change my mind by tomorrow!