Stanza 2 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Old Year! upon the Stage of Time
You stand to bow your last adieu;

Here's a major shift, as Service introduces a metaphor that will take up most of the rest of the poem. We zoom out from this one man's thoughts and feelings, and our speaker starts to talk to the passing year as if it was a person.
Specifically, he compares the Old Year to an actor, and imagines this actor standing on the "Stage of Time." The actor is taking his final bow at the end of his performance, saying goodbye ("adieu") to the world.
This nifty poetic trick is called personification, where you give human traits to an idea like a year.

A moment, and the prompter's chime
Will ring the curtain down on you.

Service has just gotten rolling on this theater metaphor.
In theaters in Service's time, there would have been a person called a prompter (a bit like a stage manager) who would have worked backstage to make sure a performance ran smoothly. Apparently one of his jobs was to ring a bell to signal the lowering of the curtain ("ring the curtain down").
So, basically, the Old Year is just "a moment" away from the end of his performance.

Your mien is sad, your step is slow;
You falter as a Sage in pain;

The personification gets more intense and personal in these lines, as Service describes the appearance of this imaginary actor.
Apparently, the old year has a sad "mien" (that's an old word for your appearance, the way you act). He's walking slowly, like a "Sage" (a wise man) who's "in pain."
Do you see how an image like this helps the poem come alive? Instead of just being an idea, the Old Year has been transformed into a character, a broken old man whose troubles you can relate to.

Yet turn, Old Year, before you go,
And face your audience again.

The Old Year is about to take off to leave the "stage," but our speaker stops him, and asks him to turn around so that his "audience" can get one last good look at him.
This pulls us back to the first few lines, when our speaker told us he was taking some time out to think about the year that has just gone by. As we'll see, the "audience" is made up of other people who have lived through this year.