All discussions about Innistrad's angels must begin with Avacyn.
Which is weird, because Avacyn is not a real angel. The other angels speak of her as suddenly appearing in their midst. Remote yet influential enough, and powerful enough, to take the leadership position among them. These angels do not know what we do: Avacyn is a vampire creation; a mechanism to ensure that the vampire, the alfpha predators of Innistrad, do not eat themselves out of existence by finishing off the human populace.
Avacyn, her power, the angels she leads, were meant to fight off vampires, demons, werewolves and other monsters and ensure humanity survives, and by so doing, to also ensure that vampires survive.
During the first two sets of the Innistrad block angels are seldom to be seen. Avacyn has been trapped beneath the Hellvault and humans are besieged. The few angel we come across show them in quite distressed poses.
As set three "Avacyn Restored" rolls in the angels return in full force.
The card Herald of War represents the dual role of angels at this point: A power unto themselves and a blessing to humans. It is fitting to show this card with another card that represents the weaponry angels bring into battle
The cards show us a glympse of their command structure. Divided into 'Flights'.
The card Defy Death gives us a glimpse of what ensues as Avacyn is freed and the angels return.
Not only do the angels retake their mantle as a counterforce to the most powerful aggressors in Innistrad, they also resume their role as humanity's divine supporters.
The next three cards share a common them: That when the angels return so to do the humans.
The card Angels of Glory's Rise show us the restoration (resurrection?) of humans and the culling of zombies.
The exile and return capability of Restoration angel coupled with Flash shows that protective quality of angels - they are able to 'blink' out allied creatures before damage can be done.
Angel of Jubilation buffs everybody (unless you have a black creature).