Line 3- Through the secrets entrusted only to the Priesthood from the messengers of the divine through their sharing of the sacred design.

"Through the secrets entrusted only to the Priesthood from the messengers of the divine through their sharing of the sacred design."


Secrets entrusted only to the Priesthood:  
The key, the Treasure is the secret
The Priesthood are those who have aspired to learn of its meaning.

Messengers of the divine:  
Mercury, Hermes, Thoth
The traveler of the 3 worlds

Sharing of the sacred design:
The key that explains the inter-connectivity of the "3 worlds"

"Secrets entrusted only to the Priesthood"

In another version of Flamel's 'Abraham the Jew' book, instead of "Priest" and "Scribe" being used, it is instead referred to as Scribe and "Sacrificer".
The Sacrificer was the one who performed the ritual sacrifice, which is also the position held by the priest.