I have friends in overalls whose friendship I would not swap for the favor of the kings of the world.

Edison contrasts the genuine loyalty of working people (“friends in overalls”) with the transactional, status-driven “favor” of elites (“kings of the world”). The line elevates character and camaraderie over rank, implying that true friendship is measured by trust, shared labor, and constancy rather than social prestige. It also reflects a distinctly American, industrial-age valuation of practical skill and plain dealing: the people who build, fix, and experiment are portrayed as more dependable companions than those who merely confer honors. As a sentiment, it functions as a rebuke to social climbing and a defense of egalitarian respect for manual workers.