If his goal is simply to preserve the superficial practice of scientific technologies, a good inspiration might be "Scientism" from Asimov's Foundation.
!A technologically advanced society find themselves beset by scientifically barbarous, but militarily overpowering forces. They openly assisted the barbarous forces in developing technology far beyond their capabilities, teaching the natives how to operate advanced machinery through religious ritual. The priests couldn't tell the science from magic, but by a strict and devout adherence to the rituals, they were able to utilize the technology.!<
If his goal is to keep powerful knowledge out of the hands of all but those who understand it well enough to use it responsibly, then yes you'll need some "initiation" or "trials" to select promising minds, and some concept of forbidden knowledge. Since your character is the bottleneck, it might be more productive to ask which knowledge shouldn't be restricted.
Ultimately, this is going to depend on your setting. Generally speaking, you have to take into consideration how powerful a piece of knowledge is, and how easy it is to implement. Powerful knowledge that requires complex technology to utilize (e.g. genetic modification) isn't much of a threat, and will be dismissed as legend more often than not. Weak knowledge that's easy to utilize (e.g. hand washing) likewise isn't much of a threat, and can propagate freely. The same applies to weak knowledge that's hard to implement, only crackpots will bother trying and won't accomplish much. Those crackpots might, however, be a good initial pool for candidates, since they're willing to put in great effort to sate their curiosity for little material gain. Further culling is necessary though, since some might just be crazed.