九变篇 NO.2：

故将通于九变之利者，知用兵矣；
将不通九变之利，虽知地形，不能得地之利矣；
治兵不知九变之术，虽知五利，不能得人之用矣。

这句啥意思：

所以将帅精通“九变”的具体运用，就是真懂得用兵了；
将帅不精通“九变”的具体运用，就算熟悉地形，也不能得到地利。
指挥作战如果不懂“九变”的方法，即使知道“五利”，也不能充分发挥部队的战斗力。

英文这么说：

The general who thoroughly understands the advantages that accompany variation of tactics knows how to handle his troops.
The general who does not understand these, may be well acquainted with the configuration of the country, yet he will not be able to turn his knowledge to practical account.
So, the student of war who is unversed in the art of war of varying his plans, even though he be acquainted with the Five Advantages, will fail to make the best use of his men.

“九变”是什么

“九变” 即今所谓作战方式与策略原则之掌握运用，当据具体情况而高度灵活机动之意。本篇首先强调通于"九变"的重要，指出只有"通于九变"，才算"知用兵"。而要做到这一点，最重要的则是要从事物正反两面的联系中去考虑问题，即所谓"智者之虑，必杂于利害"，并以"利"为准则，灵活地运用作战原则。