Tao te Ching: 56

He who knows does not speak.
He who speaks does not know.
Close the mouth.
Shut the doors (of cunning and desires),
Blunt the sharpness.
Untie the tangles.
Soften the light.
Become one with the dusty world.
This is called profound identification.
Therefore it is impossible either to be intimate and close to him or distant and indifferent to him.
It is impossible either to benefit him or to harm him,
It is impossible to either honor him or to disgrace him.
For this reason he is honored by the world.

Again, this echoes four lines from Chapter 4. It is advice to the sage meant to bring him into harmony and out of conflict with the world.

I'd rather think about the first two lines though. They're the ones that are new ground for Lao Tzu in this chapter. The true Tao cannot be told because it is hidden and nameless. One cannot name the unnamable, so someone claiming that they can obviously does not know the true Tao. The Zen Buddhists have a silent transmission of the dharma that means the same thing, and I mentioned that briefly in Chapter 43. No one can explain Zen to you, and if they say they can, then clearly they haven't attained it for themselves. The best way to transmit the dharma is by doing and by example, letting others eventually come to enlightenment on their own.

And what of the Christians?

Even a fool, when he holdeth his peace, is counted wise: [and] he that shutteth his lips [is esteemed] a man of understanding. Proverbs 17:28

The idea of opening your mouth and revealing that you don't know what you're talking about is a common one. The man who opens his mouth and says he does usually doesn't.