How do I build a narrative the whole company tells the same way?

Write one narrative, not a messaging document, and make the sales deck the artifact that carries it, because long messaging docs get filed and never used. Get the leadership team to agree on the shift in the world, the winners and losers, and the promised land before anyone touches a slide, since disagreement at that level shows up later as five different pitches. Then roll it out with a real internal launch: a briefing, a certification where reps deliver it back, and updated battlecards, discovery questions and onboarding. The test is simple, ask three people in different functions what the company believes and see whether the answers rhyme.