Copywriting vs Messaging
The medium is the message
People mistakenly use messaging interchangeably with copywriting but they're different in two specific ways.
Firstly, copywriting tries to convince someone to take (or decline to take) a specific action, usually now or in the near future. Messaging, though, is inherently more long-term and it may not care at all whether it results in a specific action.
That's because the purpose of messaging is to create new understanding or belief. Copywriting doesn't necessarily care about that.
In Brand Messaging, for example, the messages in question are more or less constrained to the brand's identity: "this is what the brand is about, stands for, has expertise in, or where it comes from".
All of which might eventually lead you, the message recipient, towards a broad, flexible range of actions/non-actions. But that's the secondary, not the primary, purpose of messaging. If you look at it that way, the long-term value of good messaging will far exceed that of good copywriting.
Secondly, copywriting is limited to written words, with some small allowance for how those words are presented with respect to spacing, font type, etc. (which quickly overlaps with design).
You write copy, you make messaging.
Sidebar: it's easy to make the case that Benjamin Franklin practiced modern copywriting during his long career as a printing press entrepreneur. He wrote not just political essays but ad copy and set the type for both; he knew the advertising business well. He experimented greatly with spacing, in a way that surprised his contemporaries yet made his publications easier to read. Perhaps this is why the Declaration of Independence, written by Jefferson and copyedited by Franklin, was visually bold compared to similar artifacts from that era. Its layout was part of its messaging ("message: the people making this declaration now observe their own bold standards").
But the point is that copywriting exists solely as words (thus it's impressive when well done), whereas messaging always consist of words, or maybe lack thereof, delivered in a specific, deliberate context. Messaging might be wrapped in any number of contextual clues, from medium, as McLuhan clued in on decades ago, to physical location, to clothing, to format, to color, to voice, to timing. And more - there's no limit to context.
The selection of speakers and performers at the presidential inauguration, for example. The selection itself was a part of the event's messaging.
It has to be said though, that this was an example of clumsy messaging revealing the myopia of the Neo-Liberal establishment. It wasn't quite as dull as the new president's speechwriting, but something was off - the word unity fell flat. Messaging doesn't always work.
So the next question becomes: should the person who writes your business copy also make your business messaging?