Moab was the small kingdom on the plateau east of the Dead Sea, in what is now west-central Jordan, and it appears in the Hebrew Bible in three incompatible registers at once.
It is an enemy: Moabite kings hire a prophet to curse Israel, Moabite women are blamed for leading Israelites into the worship of another god, and Moabite wars are recorded on both sides. It is a kinsman: Genesis derives the Moabites from Lot, Abraham's nephew, which makes the two peoples relatives in the text's own genealogy. And it is an ancestor: the book of Ruth makes a Moabite woman the great-grandmother of David, and therefore places Moabite descent inside the royal line and, for Christian readers, inside the genealogy of Jesus.
The national god was Chemosh, and the relationship between king, god and land looks structurally similar to Israel's own. The Mesha inscription, raised by a Moabite king in the ninth century BCE, describes his god as angry with his land and therefore allowing its subjection, then commanding the recovery of particular towns, with the population devoted to destruction as an offering. The reasoning, the vocabulary and the practice are recognisably the same family as the biblical ones, from the other side.
That inscription also carries what most scholars read as an early external reference to the God of Israel by name, which is why a modest stone from a small kingdom matters well beyond it.