How do you explain the difference between positioning and messaging to internal stakeholders?

Positioning is the precursor to messaging. 

If you don't know who your product is for, what it's good for and how it's different from other products in its space, then it will be very hard to come up with viable messaging. 

Put another way, positioning is the primitive, typically expressed as an internal statement (see question above re: Geoffrey Moore's framework), whereas messaging is a set of derivative assets, typically copy and value statements that help suit the needs of different channels and media (web, print, social, video, on-site activations, etc)

I generally anchor to the time-horizon and the purpose.

Borrowing from April Dunford, positioning is "context setting for prospects." Once you've established your positioning (which takes time, especially if you're pre-product market fit!), you need to be consistent over a relatively long timeframe, think 3+ years. Positioning answers the value you deliver to your ideal customer, through what differentiated capabilities, and in contrast to what competitors within a particular category.

Messaging operates on a nearer term horizon, and is how you convey your value (whether as a holistic brand or as a product line) to the market; it's the storytelling strategy. Any given campaign or piece of content needs to be laser-focused on a single persona, main point, and genuine proof points or reasons to believe the main point.

In my experience, it's likely that you (and your stakeholders) will tire of both your positioning and your message strategy before your ideal target market does... When you have the urge to evolve, make sure you're challenging this impulse and have a strategic reason to do so, such as clear message testing insights or a big shift in the competitive landscape/category, your differentiated capabilities, or the value you bring to customers.

I'd describe positioning as how we want to be perceived in the market, and messaging as the customer-facing language that proves it. But in practice, I've rarely (if ever) had this specific conversation at Momentive outside of PMM: it tends to be pretty marketing-centric. What I've learned from internal stakeholders is that what's most important to them is to be able to look at a messaging document and know what's internal framework vs. something they can use in external-facing materials, so we tend to mark things clearly in those terms when putting a new messaging resource together.

Messaging is the way you describe and present your product or service to the market. It will describe the customer or market challenge, your solution or product capabilities and the benefits provided. Positioning focuses more on what differentiates your product or service in the market. Messaging: Our product helps you automate tasks to create efficiencies and cost savings. Positioning: Our product leverages artificial intelligence to automate tasks. 

One thing I've seen work is positioning "positioning" as business strategy or a business plan versus marketing "words" we want people to think about and use.

Positioning is the company's strategy — based on research and expertise — for who we're going after (e.g., sales teams) with what category of product (scheduling automation) to solve what problems or address what jobs to be done (qualify, route, and schedule meetings via the marketing website) to achieve a business outcomes (shorten the sales cycle, improve the customer experience in the buying process, generate more eager leads, etc.). Unlike the competition, you can self-serve and launch our product for this in 30 minutes — versus weeks with technical help.

The positioning is the company's strategy for winning. It's not just marketing stuff on a page.

Sure, marketing will do things to tell this story, but the whole company will also rally around the strategy. Product will continue to differentiate us from the competition with better UX, new features, and integrations. Sales will prioritize sales-team buyers. CS will help support and track the business outcomes our customers got excited about.

Messaging, on the other hand, are the words we will all use to talk about the offering, benefits, differentiation, etc. when engaging with customers, creating ads, writing emails, drafting sales scripts, and so on.