Priest: The precepts must be obeyed!

Tidus: Like I care! (narrating) Maybe this wasn't such a good idea after
all.

Tidus and proceed to the Cloister of Trials. After solving the puzzles
to this area, Wakka appeared.

Wakka: Hey! What's gotten into you? Hey, it's okay. Only summoners,
apprentice summoners, and their guardians can enter here. It's a
tradition. Very important.

Tidus: So what about you?

Wakka: Me? I'm a guardian.

Tidus: A guardian?

An elevator platform appeared under Tidus and Wakka and they go down.

Wakka: Summoners go on a pilgrimage to pray at every temple in Spira.
Guardians protect them. The guardians in there now... One of them's got
a short fuse, and who knows what the other's thinking. Well, now that
we've come this far...might as well go all the way!
It is just a tradition passed down saying so that only Apprentice /Summoners and Guardians can enter the Cloister of Trials .Although you see Yuna enter the Chamber of the Fayth alone throughout the game, but you can return to the Chamber of the Fayth later in the game with Tidus tagging along as well.