And there's a barrel that I didn't fill Beside it, and there may be two or three Apples I didn't pick upon some bough. (line 3-5)
He has a perfectionist attitude that could be chalked up to the "Protestant Ethic," a theory that argues that people from Protestant cultures (like New England) value work for its own sake, rather than as the means to an earthly end. Work is the path to salvation. On the other hand, work is also Adam's curse. After the Fall of Adam and Eve in the Book of Genesis, Adam is cursed with having to labor for his food.
I skimmed this morning from the drinking trough (line 11)
This line illustrates how the poem is set in an earlier era. The speaker most likely lives on a farm without running water. As such, he takes his drinking water from a trough every morning. When the trough freezes in the cold, he has to skim the layer of ice off the top. Thank goodness for modern conveniences!
For I have had too much Of apple-picking: I am overtired Of the great harvest I myself desired. (lines 27-29)
The apple harvest is a yearly tradition, but that does not mean that the speaker's attitude toward the practice doesn't change from season to season, or even from day to day. The sheer repetitiveness of the activity, and the care it requires, have worn him out. He can no longer focus on apple-picking's positive aspects.
No matter if not bruised or spiked with stubble, Went surely to the cider-apple heap As of no worth. (lines 34-36)
Custom and tradition dictate that the apples that have fallen should be thrown into the apple heap, even if there is nothing else wrong with them. The apples are considered "dirty" and "corrupted," even though, as your mother would say, "There's nothing wrong with that apple! Just eat it!" Indeed, many of the fallen apples don't even have a bruise, so you could not tell them apart from the others. Still, the speaker reluctantly follows the custom – which seems to defy reason – and throws the apples in the cider-heap.