I thought it was significant that Wes mentioned being a Watcher. He did it in a context of telling truth from lies/majik. But it’s also significant because of Illyria. A Watcher trains someone else to do the fighting. Sunnydale Wes was a lousy Watcher. He failed Faith and Buffy. There was some redemption for him with Buffy in the Graduation Finale – he did stay to try to help (although he got knocked down in the first seconds of the battle and made no further contribution, thereby demonstrating his ineffectiveness). But there was no redemption for him with Faith until LA.
Me, too. I was just working on a section about that for my LJ entry that is probably never going to come to pass. It was about how all of their assignments, and the way they fit so nicely with each character's journey. I'll just put that part up here.
Each character is assigned a target from the Circle of the Black Thorn. Each target (or the way the character approaches it, or the fallout from making the mark) is, in some sense, a personal demon for the team member to whom it is assigned. Wesley must kill Vail. In part, killing Vail is assigned to Wesley because of who he is. While tending her wounds, Wesley told Illyria that one of the first things a Watcher learns is to separate truth from illusion because in the world of magicks, it is the hardest thing to do. Who else can handle this sorcerer demon?
Perhaps more significantly, Vail-as-target also ties nicely into Wesley's journey, because Angel knows Vail is psychologically vulnerable to Wes. Vail indicated as much when he confided to Angel that he sees Wesley as intriguingly unstable. Angel tells Wes that Vail suspects Wesley would betray Angel. Of course Wesley has unintentionally betrayed Angel before. The memory of this is only in his mind again, because (again) he failed to trust Angel (and I'll note here his distrust is always justifiable, I'm not criticizing Wesley, just summarizing the past*), and broke the Orlon Window, which returned the S3/S4 memories to him. This—Angel assigning Cyvus Vail to Wes—is, to me, one of the most beautiful moments of the episode, and possibly of the series as a whole, or at least in Wesley and Angel's journey together.
In giving Wesley this assignment, essentially Angel is saying, since you have failed to trust me, and betrayed me before, Vail suspects you'll do it again. Regardless of and because of the fact that you have failed to trust me—have betrayed me before, I have such faith in you, that I am trusting you to go to the one who could most help you betray me, and then justify my faith in you. I don't know if that makes any sense to anyone who isn't me. But it just brings me to tears, and Wesley's parting glance at Angel, reveals that Wes is fully cognizant of the depth of faith Angel has in him.
*Wesley's history with Angel is so complicated, that I have had to simplify it, in order to address it while maintaining any kind of flow. I completely understand why BtVS S3 Wesley didn't think the Scoobies should waste time saving Angel. I completely understand why Wesley did not trust Angel with Connor, once he started uncovering the prophecy. Angel does, too. And if I had time, I'd go into Plei's observations of how very Catholic Angel is, and tie it all in. But I can't.
Suffice it to say that Angel has frequently been grateful, in a very real sense, when those important to him have failed to trust him, or have had to betray him. He may have been hurt, and/or angry, but more than anyone else, Angel knows the dark that lurks inside him—knows what he is. He is glad Buffy "killed" him to save the world. He respects Connor dumping him to the bottom of the sea, when Connor thought Angel killed Holtz. He respects that Wes took Connor from them. He respected Gunn's early distrust of him. I keep seeing that scene from early on, when Cordelia reveals she always keeps a stake on hand. His reaction there (I can't even remember the episode) is what I'm trying to get at here. It has made him feel safer...from himself. He respects that these people did him wrong, when trying to do right.