Q:

"Do forgive me"

Good morning everyone, I am an English learner and I am reading "Dracula" by Bram Stoker.
I have a little question regarding this sentence:

"Oh, do forgive me for being so rude" pronounced by Jonathan.

What's the difference between the same sentence without the verb "do"?
I mean "Oh, do forgive me for being so rude" vs "Oh, forgive me for being so rude"
Correct me if I made a mistake. Thank you all.

A:

In English declarative sentences we can make a sentence emphatic by stressing the auxiliary verb:

I can speak English.
I can speak English.

If the original sentence doesn't contain an auxiliary, we insert the dummy auxiliary DO:

I like elephants.
I do like elephants.

Imperative sentences in English do not usually have an auxiliary verb. There are two scenarios in which we need one, and have to use DO support. The first is if we want to negate the imperative:

Move!
Don't move!

The second is if we want to make the imperative emphatic:

Excuse me.
Do excuse me.

Notice that using do in this way often makes the imperative more beseeching and less order-like. It can be seen as a polite form. However, this isn't always so, as you can see below:

Be quiet.
Do be quiet.

The Original Poster's Question

Oh, do forgive me for being so rude.

The speaker here has used do to make the imperative emphatic as a sign of politeness.

