The April 12th issue of Jinja Shinpō carried an interesting short article, written by someone in their final year of training for the Shinto priesthood at Kokugakuin University. Their concern was that, in order to avoid spreading COVID-19, many matsuri were being held with minimal attendance, often just the officiating priests, and that this was against the basic character of Shinto. They argued that jinja, and matsuri, should be open to everyone.
This is certainly a very common idea in Shinto, and in modern jinja. Most jinja do not even have gates that they can close to keep people out at night, and the idea that anyone can come to pay their respects to the kami is deeply ingrained.
However, it is not the only idea. Secret and exclusive matsuri are also an important part of the Shinto tradition. Many jinja have hereditary priests, and even hereditary ujiko, so that a person can only play a certain role in the matsuri if their ancestors played that role. This idea goes back to the early ninth century, at least, and probably earlier. Some of the matsuri are only attended by people in one of these hereditary groups. More broadly, it is not at all uncommon for certain matsuri to be restricted to the priests performing them. Perhaps the best example of this is Jingū, at Isë, where the main part of almost every matsuri at the central jinja, the Naikū and Gekū, is hidden from everyone but the participating priests.
On a different axis, while jinja are a central part of the Shinto tradition, venerating the kami in your own home, on a kamidana or at a small shrine in the grounds of your house, is also a central feature. Indeed, Jinja Honchō wants to encourage every household in Japan to do so. These household rituals are, of course, fundamentally private. People from outside the household do not normally participate, and they certainly are not open to people off the street.
It is not even easy to say which of these strands is older. Private and public matsuri both appear in the earliest sources we have, and not in a way that suggests that one was more fundamental than the other.
This is not really a contradiction, just a tension. Shinto almost never says “Anyone can attend a matsuri, but not you”. Rather, it says “Anyone can attend a matsuri, but not that one”. What is more, in principle I think anyone can create a new private matsuri, probably with the cooperation of a local priest. Having a priest purify a new kamidana is even an expected ritual.
So, which aspect is more important? I’m really not sure. I write more about the public aspects, and I know more about the public aspects — but that is because they are, well, public. It is entirely natural for me to know much less about the private and secret aspects of Shinto. All we can say is that both aspects appear to be very important.