John Mayer’s The Search For Everything was released monthly in groups of four tracks. “Changing” was released as a part of Wave One, the first of these mini-releases.

The track is an ode to John’s constant evolution. Whilst it’s about personal evolution and “following [one’s] heart,” Mayer’s music has also endured several notable evolutions, shifting from pop to blues to country-rock.

He’s confronted themes of change on previous releases. On 2006’s “Stop This Train,” he sings:

So scared of getting older, I’m only good at being young…

It seems that in the 11 years between then and now, John’s warmed to the idea of change.
During an Q&A on Twitter, he revealed that “Changing” was the most difficult record to write:
https://twitter.com/JohnMayer/status/838287720589881344