In the moment's pause I <speak of>, I saw~

[park sang joon]

The narrator recalls his adolescence.
He is an apprentice for the lawyer Mr. Spenlow.
His grand aunt and her best friend came to London after her going bankrupt.
He encountered his best friend Agnes, who came to London to meet his grand aunt, came to his apartment with her.
After a while, Agnes' father, a local lawyer, Mr. Wickfield and his partner, Uriah Heap who had been his clerck, came to.

This was only for a moment; for Agnes softly said to him, 'Papa! Here is Miss Trotwood - and Trotwood, whom you have not seen for a long while!' and then he approached, and constrainedly gave my aunt his hand, and shook hands more cordially with me. In the moment's pause I speak of, I saw Uriah's countenance form itself into a most ill-favoured smile. Agnes saw it too, I think, for she shrank from him.
[David Copperfield by Charles Dickens]
I'd like to know what is the object of "speak of."
Thank you in advance for your help.

 

[Glenfarclas]

"The moment's pause." It's presumably what he spoke of when he said "This was only for a moment," although as you have not given us the preceding sentence we cannot be certain.

 

[park sang joon]

Thank you, Glenfarclas, for your so very helpful answer.
He didn't say nothing when they came in, but thought of their appearances.
"This was only for a moment" means "Mr. Wickfield stood still for a while."
And I was wondering if the listeners in "I speak of" are the readers.

 

[Glasguensis]

Yes - we can also use "speak" when we are writing, and then we are speaking to the readers.

 

[park sang joon]

Thank you, Glasguensis, for another so very helpful answer from you.