He was a newcomer to the land, a chechaquo, and this was his first winter. The trouble with him was that he was without imagination. He was quick and alert in the things of life, but only the things, and not in the significance. (3)
The man is a newcomer to the Yukon. The narrator uses a Native American (Chinook) word to describe him, suggesting that the narrator is more knowledgeable about the Yukon than the man. The narrator then builds on this narrative distance by pronouncing judgment on the man before we've even had a chance to see him in action and judge for ourselves. What is all this about the man's trouble? Why should we care if he doesn't appreciate the significance of things? What's wrong with just wanting biscuits and bacon? Biscuits and bacon are delicious.
Fifty degrees below meant eighty-odd degrees of frost. Such fact impressed him as being cold and uncomfortable, and that was all. It did not lead him to meditate upon his frailty as a creature of temperature, and upon man's frailty in general, able only to live within certain narrow limits of heat and cold; and from there it did not lead him to the conjectural field of immortality and man's place in the universe. (3)
This quote builds on the narrator's earlier claim that the man doesn't appreciate the significance of things. Only here there's a connection between the man's lack of imagination and the fact that he might be foolishly endangering himself in the frozen Yukon. The man's inability to appreciate the significance of things makes him mistake the difference between fifty degrees below zero and seventy-five, a difference that might be enough to cost him his life.
The furrow of the old sled trail was plainly visible, but a dozen inches of snow covered the marks of the last runners. In a month no man had come up or down that silent creek. The man held steadily on. He was not much given to thinking, and just then particularly he had nothing to think about save that he would eat lunch at the forks and that at six o'clock he would be in camp with the boys. (9)
This passage shows us the man's thought process at work. He's not dumb, for starters. He can very keenly see that no one has traveled along the creek in some time. But his mind does not draw any conclusions from this, such as: hey, maybe this means I shouldn't be traveling today. Time and again, the man shows very clear perception, but then foolishly neglects to draw a helpful conclusion from it.
He did not expose his fingers more than a minute, and was astonished at the swift numbness that smote them. It certainly was cold. He pulled on the mitten hastily, and beat the hand savagely across his chest. (13)
The man continues to be surprised by how cold it is. As readers, we don't know what to make of this, since we might expect a newcomer to the Yukon to be much wimpier. We expect someone who's used to the cold to not mind it so much. But this man seems not to pay much attention to anything. His brain seems to be missing the part that draws wider conclusions from isolated pieces of information (kind of like the skill you learn when analyzing literature, wink wink).
He pictured the boys finding his body the next day. Suddenly he found himself with them, he came around a turn in the trail and found himself lying in the snow […] It certainly was cold, was his thought. (40)
This quote might suggest that when the man is about to die, he finally develops a little imagination and projects his mind completely beyond his freezing body. On the other hand, the repetition of "It certainly was cold" brings us right back to the man's simple, foolish thinking at the beginning of the story. There's a lot of ambiguity here, and as a reader, you might need to decide for yourself what the story is suggesting in these lines.