The sentencing goes blithely on its way
And takes the playfully objected rhyme
As surely as it takes the stroke and time
In having its undeviable say.
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Frost is writing about how a poem comes about for him. He matches what he had to say with end-rhymes as a form of play, then finds a pattern which seems right and from which he is unwilling or unable to break away (interesting that I too find myself writing in verse!)
In short sweet words the presentation of a poem about the poem.