What information we get about Gilead, we get from the woman currently known as Offred—even though she's only allowed a really limited view of the world. And we mean that literally: she's not allowed to make eye contact with most people.
We see Gilead as "Offred" sees it; we interpret it as she interprets it; and our only knowledge of it comes from the tidbits she gives to us. From a dramatic or plot standpoint, we only discover the narrator's history and the events that led up to the foundation of the Republic of Gilead as she reveals them, almost as an aside to her narrative about what's happening to her at her third posting (the Commander's home).
We have to trust her about Gilead and what happens to her. At the same time, that trust is continually undermined by her comments about how she wishes she could change the direction of her story and admissions about how she has changed it, as well as constant evasions and the use of pseudonyms. She even says at one point, "This isn't a story I'm telling," before turning around in an about-face and saying, "It's also a story I'm telling, in my head, as I go along" (7.34-35).
Frustrating? Sure. But not nearly as frustrating as being stuck in Gilead.