"Do It Now" revisits one of the favorite catchphrases of Paul McCartney's father. He explained to The Sun
that if he told his dad say: "I'll do it later," he'd reply: "No, do it now."
McCartney added that "this do-it-now thing" had been in his head for a long time as a song idea. Then he started imagining: "OK, I'm on a journey. I've been invited to go somewhere and if I don't do it now, I may never get to this place."
The ex-Beatle eventually came up with a song about a make-believe journey where he's prompted to start traveling "now, while your vision is clear."