it shall affect

[suprunp]

“We would not presume to dictate what you should or should not do. However, as your friends and allies, have we not earned the right to offer our advice upon such a weighty matter, especially when it shall affect us all?"
(C. Paolini; Inheritance)

What does 'shall' express here? Is this just an archaic usage of it?

Thanks.

[Rover_KE]

I wouldn't call it an archaic usage.

Perhaps oratorical, rhetorical or declamatory.

Rover