[… ] the fire that breaks from thee then […] (10)
As the bird makes a dive toward the ground (he must have spotted a mouse or some other small animal to catch), the red on his chest flashes like fire. But the "fire that breaks from him" sounds kind of dangerous, like he's a falling star or a crashing airplane or something.
[…] shéer plód makes plough down sillionShine […] (12-13)
The speaker says that even a simple plough is beautiful—when it's well used, the steel of it gets all shiny. The speaker seems to be suggesting that even well-worn everyday things, like farm tools, can appear beautiful if you look at them in the right way.