Levine's purpose for this expression is to identify the personality traits of determination, perseverance and strength. Because Levine used just one random man out of a larger group and compared him to his own brother, what he's really saying is that these character traits of determination, perseverance and strength (when it comes to work) are common traits for men to have. .
The clichés "grin and bare it- and "the job's not worth doing unless it's done right- come to mind in terms of these masculine traits. This is not a sexist observation in the least; it's simply an observation of the meaning behind Levine's metaphor. For had there been even one woman standing in that line, than the image of masculinity would be destroyed and it would be very hard to connect the line of men with gender related issues. .
The "sad refusal to give in- suggests that this man, just one among many more like him, will continue to stand in the cold rain and wait for a job that may not even come. Levine's purpose is to express that men characteristically focus on goals and not journeys. Society, family, etc. have taught the speaker that it just doesn't matter what has to be done to get a stable, worthy job. Judging by the expression, these men don't necessarily want to be where they are. (Both literally and figuratively.) However, some notion has been placed in their minds that they need to be provider and they need to remain strong even if it means having a job that they have no interest in and no passion for. .
Although the man with the stubborn grin reminds the speaker of his brother, Levine has an epiphany in regarding work and its true meaning. He realizes that his brother is leading a very different life than the men on line waiting for jobs. We don't know exactly what the brother is doing in terms of a job, but we do see that he "works eight hours a night so he can sing Wagner, the opera (the speaker hates) most, the worst music ever invented.