Back in a time made simple by the loss Of detail, burned, dissolved, and broken off Like graveyard marble sculpture in the weather (2-4)
A rolling stone may gather no moss, but a gravestone, or marble sculpture, is subject to all that and more: weather, time, fire, you name it. Man may make it, but nature unmakes it with time.
The ledges show lines ruled southeast-northwest, The chisel work of an enormous Glacier That braced his feet against the Arctic Pole (15-17)
If you're talking about Man's time on the earth it's a nanosecond compared to the lifespan of a glacier. Here, Frost personifies the glacier as a kind of sculptor of the earth, and he's still hanging around just to blow some haunting coolness down your collar.
As for the woods' excitement over you […] Charge that to upstart inexperience. […] They think too much of having shaded out A few old pecker-fretted apple trees. (23-28)
You may remember from science class that you can gauge the age of a forest by the kinds of trees that grow there. Which is essentially what Frost is mentioning here. Imagine that man has cleared the brush and trees enough for a building site and a field for an apple orchard. Left untended, the wild plants and trees grow back. These are still young (full of "upstart inexperience") but they've grown tall enough to shade out the apple trees, which, with nobody to defend them, are pecked to pieces by woodpeckers anyway.
But only a belilaced cellar hole, Now slowly closing like a dent in dough. (46-47)
There's an inevitability to the overgrowth in this image. Nature grows rampant, now that those who civilized this place are long gone. That's Nature 1, Man 0.
A brook that was the water of the house, Cold as a spring as yet so near its source, Too lofty and original to rage. (50-52)
If nature is often destructive, it can also be redemptive. Hey, this brook is what kept the people of the house alive and sustained, and it can do the same for you. Why not drink up?