by perfalbion
You're reading the walkthrough a bit incorrectly. What it says is:"While in a monastery, you may decide to try to burn it down as your
Action for the turn (if you haven’t already taken your action for the
turn – and especially not after interacting in the monastery!)."
So on Turn X, you interact at the monastery and grab a unit, an AA, some healing, or some combination of the three. On turn X+1, you burn it down because you haven't used your action yet for the turn.