In the Things sourcebook for Chill 2nd Edition, an in-character preface by Rev. Samual D. Farthings concludes with, "Remember, if all else fails, God and SAVE are on your side." That line, I think, crystallizes what Chill is about for me.
Horror games aren't exactly thin on the ground these days. They weren't as common in the 80s when Pacesetter released the first edition of Chill, and they were gaining ground in 1990 when Mayfair released the second edition, but they're everywhere now. You can play doomed investigators in Trail of Cthulhu or Call of Cthulhu. You can play members of the occult underground in Unknown Armies. You can play monsters of many different stripes in the World of Darkness. And, of course, licensed settings like Supernatural give you the chance to jump into the worlds of your favorite horror properties. (Feel free to comment and tell me about your favorite horror game, I just listed a few here.)
So as we're redesigning Chill for our third edition, we're looking for something to hang the game on. It has the be the setting, because the system, while it's getting cleaner all the time, is just a game system, and that's never going to be what gets someone to pick up a game. And that setting means SAVE.
In the 2nd Edition, SAVE was having some problems. It was reeling from the loss of the archives in Dublin and unprecedented levels of envoy loss (10% of their membership a year, and while recruitment was keeping pace, that's still a horrific amount of loss). As we're designing the 3rd edition and thinking about how SAVE has evolved, we have to consider advances in technology. We have to think about how SAVE is still a functional entity, if it was losing so many people. And we have to think about how it operates day to day. I've draw parallels between monster hunters and revolutionary (or even terrorist) cells before, not to disparage SAVE's motives, of course, but because that's how they have to function. SAVE is smaller than the enemy. It doesn't have access to information or resources in the amounts it needs. But SAVE soldiers on.
Why? Because they're on your side. They're on our side. The good reverend mentions God, but the Chill setting isn't an explicitly Christian or even theistic one. SAVE envoys do what they do for a variety of reasons, but at the end of the day, they do it because the thought of not doing is too horrible to contemplate. They do it because someone has to. They do it because they can. They do it because they're people, and they are unwilling to abandon others to the Unknown.
Being a SAVE envoy is largely thankless, it's highly dangerous, and it often ends in horror and death. And the envoys open those activation letters and go out into the dark anyway, because they're on your side.
That's a decent hook, I think.