When are doors meant to be Armed?

[SV_741_India_Bravo]

Here at Saudia,all the doors are armed when boarding has ended and when the ground crew leaves the plane,However during taxi the captain /FO say:
"Good Morning/Evening Flight Crew.All doors to flight and be seated for take off"

I dont understand why pilots say good morning/evening.I thought the entire crew met in the crew room?

Anyway,after arrival when the plane has parked,the captain/FO say:
"All doors to ground"

Its the same with PIA too.