This Maxim is one that tells us to recognize when it is appropriate to speak or not to speak, both within ritual settings and about them. It does not tell us that we should be completely silent during worship, but that we should not cause interruptions or disruptions by speaking out of turn. We should also keep the Mysteries secret (as we re-create or re-discover them) by not speaking of them to those who have not undergone them. This is not as easy as it would seem in this era of easy access to information, but is still possible.
These Mysteries are things that cannot be explained, but only experienced. This is one of the reasons that religious silence is so important. We must not bias the expectations of those who follow in our footsteps in experiencing them. We must maintain our silence even in the face of people asking about our experiences. The Eleusinian Mysteries were only one of the Mysteries of ancient times, even if they are the best known. And even now we don’t know exactly what went on, so well did the ancients follow this Maxim. If we are to imitate them, we must imitate them even in this.