What is the one thing that the elders of K'un-Lun value above all else?

Question

In "Mean Right Hook" (Marvel's The Defenders, S01E02), Madame Gao and Alexandra have a conversation in which Alexandra mysteriously talks about one thing that the elders of K'un-Lun have valued above all else, from the beginning.

ALEXANDRA: If they wanted to take this one from us forever, they would have destroyed it, not protected it, which means it's not a wall.

MADAME GAO: I've seen it!

ALEXANDRA: It's a door. It's meant to be opened.

MADAME GAO: By what?

ALEXANDRA: The conviction of the elders of K'un-Lun was always unwavering. They think it's a virtue, but in the end, all it ever did was make them predictable. They've locked it away, but a lock is not a lock without a key. And from the beginning, they have valued one thing above all else.
_{—"Mean Right Hook" (Marvel's The Defenders, S01E02)}

What is the one thing?

Answer 1

My interpretation is that its...

Iron Fist

..or at least the power of Iron Fist.

They're talking about opening a door...and, as we find out, the one thing that can open the door is the power of Iron Fist so it makes sense in the context of their conversation.

When Alexandra captures Stick, he thinks she wants Iron Fist to join her army or use him as a weapon but she says to Stick..

"After a lifetime of serving K'un-Lun you don't even know what he is!"

They spend a lot of time trying to capture Danny so that he can open the door. An Iron Fist sealed the door and only another can open it.

Answer 2

It couldn't be the Iron Fist, nor his power. It's only the key to open that valuable thing. Fist or his power was not the thing being locked away by the wall.

I think those elders valued above all is Good in people's lives and Life being flawlessly go forward as it meant to be.

Hand stand against both. They use their power, abilities and resources to do bad, evil things. and they've found a substance that has the ability to alter the flaw of life from how its intended. Things like resurrect from the dead, living forever/immortality.

What the elders locked away was the very substance that helped the members of hand to alter that flaw of life.

What Iron Fist did was locked it away so hand couldn't get that substance. No Iron Fist would deliberately give it to hand, so only another Guardian has the ability to open it