The rule of the Zagwe Dynasty is the correct answer.
The event that helped give Christianity a permanent place in Ethiopia was the rise of the Zagwe Dynasty. Even though, during colonialism, Europeans were the ones who spread Christianity in Africa, Ethiopia wasn't included in that. The adoption of Christianity in Ethiopia happened via merchants that resulted in the conversion of Frumentius and consequently led him to become the first bishop in Aksum. The Zagwe dynasty kept the cultural traditions of Aksumite state and let Christianity remain as the official religion in that country.