In raiding and plundering be like fire,
Cf. _Shih Ching_, IV. 3. iv. 6: 如火烈烈則莫我敢曷 “Fierce as a
blazing fire which no man can check.”
in immovability like a mountain.
That is, when holding a position from which the enemy is trying to
dislodge you, or perhaps, as Tu Yu says, when he is trying to
entice you into a trap.