Here's a bit of what Lowell had to say.
The arts do not progress but move along by surges and sags. Frost, born in 1875, was our last poet who could honestly ignore the new techniques that were to shatter the crust. He understood the use of tools, often wonderful tools, that five or ten years later would be forever obsolete. . . .
Frost had a hundred years' tradition he could accept without question, yet he had to teach himself everything. Excellence had left the old poetry. Like the New England countryside, it had run through its soil and had been dead a long time. Frost rebuilt both the soil and the poetry: by edging deeper into the country and its people, he found he was possessed by the old style. . . . Step by step he had tested his observation of places and people until his best poems had the human and seen richness of great novels. No one had helped him to learn, and now no one could because no one wrote better.