An enemy apostle capable of infiltrating the 'Disciple's Sanctuary', no doubt have substantial influence within the organization. Even the weakest pawns have plenty of subordinates at their disposal, not to mention those competing to become apostles.
Lin Xun is an exception. He is an undercover, without a single soldier under his command.
Backed by an official organization, he could mobilize a large number of official apostles to infiltrate the New World.
However, after discussing with Li Long, his new superior shot down this appealing but dangerous plan.
Now that Lin Xun has become the twelfth apostle, even if a large amount of official apostles were sent undercover to the New World, they would only work under him, and couldn't possibly obtain more information than him.
Moreover, the infiltration of a large number of ' unknown' apostles into the New World could arouse attention and be more detrimental to him.