Question: The following stanza is from Robert Frost's *Into My Own*:

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> One of my wishes is that those dark trees,  
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>  So old and firm they scarcely show the breeze,  
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>  Were not, as ’twere, the merest mask of gloom,  
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>  But stretched away unto the **edge of doom**.
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(Emphasis mine.)

I am guessing that the "edge of doom" is referring to the end of time -- as in, The trees are stretching into the end of time and space. Is this reading correct? Where does the phrase the "edge of doom" come from? At first when I read it, I thought that the "edge of doom" was a dark reference (similar to "mask of gloom"), but it seems to be closer to a wedding vow, such as "Our marriage will last unto the edge of doom".

Answer: 
Your reading of the poem makes sense. It might help to know that the dark trees are symbolizing the future in this poem. The second line tells us that these trees rarely show a breeze. This means that we cannot predict the future. 

In the fourth line, Frost expresses his wish that those dark trees in the first line were stretched away to the edge of doom. This means that he hoped that the future is stretched far away. So, the edge of doom means here far away (in time). This seems consistent with your view, since it is also used in that way in the sentence you quoted, "Our marriage will last unto the edge of doom". 

Based on: [Analysis of "Into My Own"](https://letterpile.com/writing/Robert-Frosts-Into-My-Own-Analysis).
The phrase “the edge of doom” comes from Shakespeare’s [sonnet 116](https://archive.org/details/shakespearesson01shakgoog/page/n108/mode/2up):

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> Loue alters not with his breefe houres and weekes,  
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> But beares it out euen to the edge of doome
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“Doom” means “fate” or “judgement” and here it is being used with the meaning:

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> **Doom, *n.*, 6.** The last or great Judgement at the end of the world
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> *Oxford English Dictionary*
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So that “to the edge of doom” means “until the end of the world”.

In the context of ‘[Into My Own](https://www.bartleby.com/117/1.html)’ the phrase turns the dimension of space (the trees stretching away into the distance) into a metaphor for the passage of time until the end of the world, and the speaker’s journey through the trees into a metaphor for his life and poetic career. And just as the speaker in Shakespeare’s sonnet says that true love never alters, so the speaker in ‘Into My Own’ says that *he* will never alter:

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> They would not find me changed from him they knew—  
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> Only more sure of all I thought was true.
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One way to read this is that the speaker is determined to stick to his own style of writing poetry, regardless of the judgement or “doom” of his critics.