For those that haven’t experienced the joy of Tolkien’s writing, this is a reference to the Elvish inscription on the Doors of Durin in The Fellowship of the Ring, that is simultaneously a riddle and literal instructions on entering.
> The Doors of Durin, Lord of Moria
but as the Tolkien Gateway explains:
> The name Moria means "Black Chasm" and was a derogatory description of the place which the Dwarves did not like, and was given after Durin's Bane took over the city in the Third Age. It is therefore a mystery why that name appears on an inscription made in the Second Age, and made in consent with the Dwarves.
The most common "mitigating explanation" I see is that Tolkien, the "translator," perhaps used the name the reader would be most familiar with (Moria) instead of the city's real name (Khazad-dûm) when transcribing the door's inscription.
The friendship between an Eleven and Dwarven kingdom was kinda rare.
And thus, speak friend and enter
Friendships between the elves and dwarves are as a result considered very special, which is why Gimli and Legolas's friendship in The Lord of the Rings is such a big deal.
[0]: https://www.imdb.com/title/tt0120737/ [1]: https://en.wikipedia.org/wiki/The_Lord_of_the_Rings:_The_Fel...
OP referenced "over 90% of HN readers", who are notoriously out-of-the-mainstream nerds[0], so he probably was referring to The Lord of the Rings (1978) [1] which grossed $33.7 million (which seems a lot less than the 2001 film, but is pretty similar as a multiplier on its budget.)
[0] https://www.example.com/what-you-thought-this-was-a-real-sou...
[1] https://en.wikipedia.org/wiki/The_Lord_of_the_Rings_(1978_fi...
Obviously there's a percentage that hasn't seen/read it if you haven't either.
Speak, friend, and enter.
Speak "friend" and enter.
Without punctuation it would be a pun in addition to being a riddle and the instructions.