Oddly enough the inspiration came from a Televangelist. Point is Lennon's songs were just words he cobbled together. He said as much in the film Imagine.
Wikipedia:"The inspiration for the lyrics came from late-night television. In December 2005, May Pang told Radio Times: "At night he loved to channel-surf, and would pick up phrases from all the shows. One time, he was watching Reverend Ike, a famous black evangelist, who was saying, "Let me tell you guys, it doesn't matter, it's whatever gets you through the night." John loved it and said, "I've got to write it down or I'll forget it." He always kept a pad and pen by the bed. That was the beginning of 'Whatever Gets You Thru the Night'."
He was different at the end of his life from what he was years before.
Who's to say what he would have been if he'd lived longer?