The High Priest merely provided a basic explanation of what these young Druids needed to do; he did not divulge the specifics.
Because not every one of these youths could possibly infiltrate the Holy Mountain, and even if they did manage to get in, there was no guarantee that they would receive certain treatments or gradually complete his plan.
Therefore, they would have to wait until the actual time came to discuss specific details, and if this operation did not go smoothly, he would even need to prepare for the next action twenty years later. Naturally, he couldn't disclose the exact plans to these youths lest they accidentally leak information and expose the agents they had planted on the Light Holy Mountain.
