Even after Christianity had begun to be embraced by the masses in the 4th century there was a certain reticence regarding the Mysteries. St. Gregory the Theologian, for example, chastised those who "fling that which is holy to the dogs, and cast pearls before swine, by publishing divine things in the hearing of profane souls." (Oration 2, 79) And Sts. Basil and Cyril of Jerusalem speak likewise:
"And as to the other customs of baptism from what Scripture do we derive the renunciation of Satan and his angels? Does not this come from that unpublished and secret teaching which our fathers guarded in a silence out of the reach of curious meddling and inquisitive investigation? Well had they learnt the lesson that the awful dignity of the mysteries is best preserved by silence. What the uninitiated are not even allowed to look at was hardly likely to be publicly paraded about in written documents." - St. Basil the Great, On the Holy Spirit, 27
“These mysteries, which the Church now explains to thee who art passing out of the class of catechumens, it is not the custom to explain to heathen. For to a heathen we do not explain the mysteries concerning Father, Son, and Holy Ghost, nor before Catechumens do we speak plainly of the mysteries: but many things we often speak in a veiled way, that the believers who know may understand, and they who know not may get no hurt” - St. Cyril of Jerusalem, Catechetical Lectures, 6, 29
Even in the liturgy today people say: “I will not speak of Thy Mystery to thine enemies”. Yet people freely talk about all manner of things, to pretty much everyone. At what point did this secrecy begin to recede? And is Christianity better or worse for leaving behind the tendency to not speak so openly?