Well, here's what I managed to write while almost falling asleep. Sorry if it's crap.
Sisters, valued allies!
I do not know how how many of us remain at this point. Of the millions who stood to hold Ophelia VII we might well be the last Imperial forces to defend this world. I want to speak to you as one of those who may change history in the coming days, who have already changed history in the days past. I speak to my sisters, as a sister.
I do believe that every just citizen of the Imperium would give everything to be in our place. No matter the outcome, billions will wish to have had the chance to fight amongst us.
Look to the sister at your side - could any of us ask for better company in the coming battle?
You know that our situation is grim. Large parts of our holy shrine world have been swallowed by the warp, daemons defiling its surface this very second. Some unnamed horror twisting it to its whims.
I do not need to educate you about the tide of heresy that is sweeping across our beloved world, worse than anything we could have ever anticipated. Worse than anybody would have dared to suggest.
But our enemy made a fatal mistake. He revealed himself to us, and all of us know just too well that if left unchecked, heresy will grow and corrupt. If our enemy had been allowed to grow unchecked, if it had remained undisturbed just a few more days, my sisters, we might just as well be facing a second Eye of Terror.
Instead, we have been given to save the Imperium from a fate that might have well spelled hardship for ballions, if not its end.
Of all the billions of humans in the galaxy, only we have been found worthy to defend Emperor and Imperium this day.
As I speak to you, my sisters, our enemies are busy fighting each other. Such is their way, and it has always been their weakness. We, however, have preserved our strength as well as we could. We have brought allies, we have gathered those who remain of us.