The description for Suasion says “It is a Persuasion skill for the clergy”.
In the list of DoW tactics Suasion is listed explicitly for Obfuscate and Rebuttal.
Persuasion is listed for Body of Argument, Feint, Point and Rebuttal.
http://burningwheel.org/wiki/index.php?title=Downloads#Burning_Wheel_Gold_DoW_skill_matrix
If you don’t know Persuasion, does opening Suasion allow the use of all the Persuasion tactics as well?
I would only allow it if it was a task suitable for the intent.
In this case the intent would need to be a religious argument appropriate to the Statement of Purpose.
If my Statement of Purpose was “In your imminent death you will leave your lands to the church” and my point was “Giving your lands to the church will save your otherwise tainted soul in the afterlife” then I’d be all for it.
Otherwise I’d not allow it as a violation of task/intent. The player is responsible for framing their purpose suitably.
But that interpretation might be unique to me.
I always regarded the fact that Suasion didn’t appear on all the skills Persuasion did as an oversight and treated it, like the skill description says, as “Persuasion for the clergy”. But it’s really only usable if you can make the DoW relevant to the Church or Faith or whatever–and it should color your arguments, too.