Today I’ve crossed on the ferry from the Isle of Mull to the bustling harbour town of Oban on the Scottish mainland. I’m heading east now along Glen Lonan, a quiet valley meandering between low rocky hills covered in birch and bracken, and I am reflecting on Aidan’s call to the people of Northumbria in the seventh century AD, through the lens of Isaiah’s call to the people of Israel in the eighth century BC…