The tremendous significance lies in what we dared not tell ...

[longnguyen1994]

Indeed, I flatter myself that even in the midst of our distress, utter bewilderment, and soul-clutching horror, we scarcely went beyond the truth in any specific instance. The tremendous significance lies in what we dared not tell—what I would not tell now but for the need of warning others off from nameless terrors.
Source: At the Mountains of Madness By H. P. Lovecraft

Context: a man is confessing that an earlier report of his wasn't truthful.

I don't get the phrase "tremendous significance" here. It feels like there's something missing in this sentence, making the meaning hard to get, but I can't quite put my finger on what exactly is wrong with it. Maybe it should have been "tremendous significance of <something>"?
Could someone help me please?

 

[SoothingDave]

He's talking about the significance of the untruthfulness he is confessing to.

There's an understood "of what we did" that is left unsaid.

 

[longnguyen1994]

He's talking about the significance of the untruthfulness he is confessing to.

There's an understood "of what we did" that is left unsaid.

I'm still a bit confused about your explanation. Could you put the phrase "the significance of the untruthfulness" in simpler terms?

 

[SoothingDave]

They lied, right? Mostly by omission. That was significant.