Really? "God Only Knows" isn't even my favorite Beach Boys tune, and I'm a big fan.
But the song has gotten all sorts of "ink" on the fiftieth anniversary of the famous album's release. From Rolling Stone:
According to a 2015 Guardian interview, Wilson claims that he and Tony Asher composed the song in just 45 minutes. "We didn't spend a lot of time writing it," confirms Asher. "It came pretty quickly. And Brian spent a lot of time working on what ended up being the instrumental parts of that song. But the part that has lyrics really was one of those things that just kinda came out as a whole."
Author Jim Fusilli theorized that the song's title was born out of a love letter Wilson wrote to his wife Marilyn in 1964, signing off with "Yours until God wants us apart." Whatever the true genesis, this reference to God created a dilemma for the two collaborators. "We had lengthy conversations during the writing of 'God Only Knows,'" remembers Asher. "Because unless you were Kate Smith and you were singing 'God Bless America,' no one thought you could say 'God' in a song. No one had done it, and Brian didn't want to be the first person to try it. He said, 'We'll just never get any airplay.'" Though a handful of Southern radio stations banned the song for blasphemy, it was warmly received nearly everywhere else.
And from Wikipedia:
Brian originally intended to sing lead vocal on "God Only Knows" but after the instrumental portions of the song had been recorded, Brian thought [his younger brother] Carl could impart the message better than he could. Brian reflected in October 1966, "I gave the song to Carl because I was looking for a tenderness and a sweetness which I knew Carl had in himself as well as in his voice. He brought dignity to the song and the words, through him, became not a lyric, but words." At the time, it was rare for Carl to sing lead on a Beach Boys song.