Is it silly that a monk spent 15 years producing an illuminated copy of a text he did not understand? From a materialist perspective, yes. What about a theist perspective? Through the dark ages, entire works of text from the ancient days were protected, guarded, and studied by monks and abbots. For a thousand years after the fall of Rome, these works were guarded and meticulously preserved despite the content of their text often being a mystery. As recently as the 1980s and 1990s, ancient manuscripts written hundreds of years ago in languages no one speaks have been found in old church basements. Entire cultures and arts have been resurrected from the dead because information once deemed useless was preserved anyway.
Off the top of my head, I can cite the HEMA martial arts as an example. An entire codified system of combat resurrected from 600-year-old manuscripts because a warrior-poet historian found a few preserved books in forgotten basements.
It is rational to throw away useless traditions and information. Surely. It would require an act of faith to value those things not for the now, but for some indeterminable moment in the distant future. One can argue, then, that rationality is not a basis for a civilization. Rationality doesn’t build temples, preserve history, or identify a cultural foundation.