Comma after 'now'

[Nonverbis]

• Now, listen to what she's saying.
• Now, the next point is quite complex.
• Now come and sit down.
• Now let me think…

Examples from here: https://www.oxfordlearnersdictionaries.com/definition/english/now_1?q=Now


Could you tell me why sometimes a comma is put but sometimes it is not?

 

[jutfrank]

When now is used as a discourse marker, then it typically comes at the beginning of an utterance, followed by a pause (a comma if transcribed). As a discourse marker, it's often a way to ask the listener to pay attention to a coming instruction, or to a new important piece of information, or to a change in direction.

If the word now is about time, then it isn't a discourse marker and doesn't need to be punctuated with a pause/comma.

 

[Nonverbis]

But these cases seem all to be discourse makers.

 

[jutfrank]

The first two are. The second two aren't.

 

[Nonverbis]

I can't catch your idea.

Could you clarify what are the second two variants?

 

[emsr2d2]

I can't catch don't understand your idea post/explanation.

 

[jutfrank]

Imagine someone giving another person a series of orders:

Go over there.
Now go over there.
Now come and sit down.

The word now is modifying the verbs, telling the listener when to perform the order. It could equally go at the end of the instruction.