"Progress" is the first time the first season of Deep Space Nine made it known that ordinary brilliance was possible. In terms of importance, it was eclipsed a few episodes later by "Duet." But it's an experience that in its own way is just as essential.
Kira was a hothead who loathed her assignment working with Starfleet to normalize things for her fellow Bajorans. She believed her own people could figure it out on their own, crawling from the wreckage of the resistance fought for decades against the Cardassians. She naively believed that the Bajorans would be able to settle their own affairs.
"Progress" was her best indication to this point that this was simply not going to be the case. She's assigned to help an old man relocate after it's deemed his land will be more valuable used for things other than what he's been doing with it. Surprising to Kira is the fact that the old man doesn't want to leave his home, no matter what others think. She spends the whole episode trying to figure out how to deal with the old man's stubbornness.
It's all about the moral complexities inherent in sticking around the same place and dealing with the same problems. That's what the series was supposed to accomplish from the start. As Bajoran episodes go, this one plays it safe by keeping Kira firmly at the center of the story, no religious matters required, no soft-spoken figures threatening to put the audience to sleep. This is an episode that could only happen and work on Deep Space Nine. Other series have ambiguities to handle, but they get to leave at the end of the episode. Everything begins to change for Kira as a result of "Progress."
Strangely enough, though the title might be considered cynical, the episode isn't, and that's a tone the series miraculously managed to maintain throughout its run.
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Memory Alpha summary.