your compactness that of the forest.
It is hardly possible to take 徐 here in its ordinary sense of “sedate,” as Tu Yu tries to do. Mêng Shih comes nearer the mark in his note 緩行須有行列 “When slowly marching, order and ranks must be preserved”—so as to guard against surprise attacks. But natural forests do not grow in rows, whereas they do generally possess the quality of density or compactness. I think then that Mei Yao-ch‘ên uses the right adjective in saying 如林之森然.
18. 侵掠如火不動如山
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.
19. 難知如陰動如雷霆
Let your plans be dark and impenetrable as night, and when you move, fall like a thunderbolt.
The original text has 震 instead of 霆. Cf. [IV. § 7]. Tu Yu quotes a saying of T‘ai Kung which has passed into a proverb: 疾雷不及掩耳疾電不及瞑目 “You cannot shut your ears to the thunder or your eyes to the lightning—so rapid are they.” Likewise, an attack should be made so quickly that it cannot be parried.