Cyril of Jerusalem
St. Cyril’s Catechetical Lectures are not intended for all readers; they are specifically directed toward those ready to receive exorcism, baptism, chrismation or confirmation, and first communion. The Procatechesis, and first eighteen lectures were delivered before baptism; the last five lectures were delivered after baptism.
In the early Church, coming out of the persecutions of the first three centuries, being recognized as a legal institution for the first time, it appears that the process of catechizing had developed into a somewhat lengthy practice, possibly lasting three years or longer. Small, children were baptized, usually by a combination of effusion and immersion, without catechizing: based on the confession of their parents. Older children and adults were catechized. The yearly cycle was focused on conducting baptisms just before Pascha (Easter), so that the newly baptized might receive their first communion at Pascha. So, by whatever process candidates were deemed ready for baptism, St. Cyril began his lectures with them specifically during Lent: the other catechumens were excluded. However, once the lectures were reduced to published writings, it was no longer possible to prevent anybody from reading them.
St. Cyril’s stated purpose in such a delay was not to make Christianity into a secret society. His only concern was that too early exposure to certain truths could be harmful: the rudiments had to be learned first. So, please don’t read these lectures if you’re not ready.