On page 16 of the Guide to Pathfinder Society Organized Play there is a special note regarding clerics of Irori which states:
"in Pathfinder Society Organized Play, clerics of Irori receive the Improved Unarmed Strike feat as a bonus feat so they can use their deity’s favored weapon (unarmed strike) without provoking an attack of opportunity."
Does this apply to clerics of Calistria, for whom the favored weapon is a whip, and if not, why not?
If you are asking about weapon proficiency in general, there is this from the core book, bolding is mine:
Quote:
Weapon and Armor Proficiency: Clerics are proficient
with all simple weapons, light armor, medium armor, and
shields (except tower shields). Clerics are also proficient
with the favored weapon of their deity.
If you are asking about AoO, then seeker answered that, as whips do not provoke one.
Of all of the deities, Irori's favored weapon actually didn't grant the cleric anything as (1) the cleric already has unarmed strike and (2) an unarmed strike provokes an attack of opportunity. The intent with Irori was that a cleric of Irori could use her fists without provoking, hence the addition of the feat.
Calistria grants her clerics the use of the whip, an exotic weapon they wouldn't normally be proficient with. Whips used by clerics of Calistria function normally, meaning they provoke as a ranged weapon.