Obadiah was a prophet (holy man). The Book of Obadiah is in the Bible (Old Testament).
The Book of Obadiah contains a short message about the country called Edom. The people from Edom were relatives of the people from Israel. But the inhabitants of Edom refused to help when the people from Israel suffered. So, God would punish the people from Edom for this evil deed. God would destroy their country.
In the future, people who trust God will live in Edom.