In "Stopping by Woods on a Snowy Evening", how would I describe the meaning of isolation in this poem?

You have identified one of the themes implicit in this
poem. What is interesting though is that loneliness is normally portrayed as a negative
emotion, but here, Frost definitely seems to portray it as something that the persona of
this poem craves and wants. The first stanza tells us that he is alone by some woods,
with the owner of those woods far away:

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He will not see me stopping
here

To watch his woods fill up with
snow.

The speaker seems to be
entranced by the beauty of the falling snow and the woods, which is why he is stopping
on his journey by himself at night.

The key stanza is of
course the last stanza, which makes evident the speaker's attraction of the woods and
his desire to stay, but also the recognition that he must move
on:

The woods
are lovely, dark, and deep,

But I have promises to
keep,

And miles to go before I
sleep,

And miles to go before I
sleep.

This, to me, makes the
symbolic meaning evident - Frost is writing about the desire to die but at the same time
he recognises that it is not time yet as he has a lot of responsibilities that he needs
to fulfil. However, he is free to enjoy the emotion of loneliness at times like this
where he takes "time out" from the responsibilities of life to reflect on the beauty of
nature.