Why do Marines say till Valhalla?

Why do Marines say till Valhalla?

To be selected into Valhalla was your reward for valor, bravery, courage and an unyielding devotion to your fellow man in combat. In common parlance, Valhalla was the heaven open to warriors who died bravely in the Norse religion. Among warriors, ancient and modern, “Until Valhalla” means, “I am with you until death.”