《旧五代史·后梁·列传十二》
军队开到天井关，牛存节对各位将领说： 此次出征，虽然不是奉行皇上诏旨，但泽州为要害之地，不可让它失去。 
师至天并关，存节谓诸将曰： 是行也，虽不奉诏旨，然要害之地，不可致失。 
When the army arrived at Tianjing Pass, Niu Cun-jie told all the generals: "This expedition, although not carrying out an imperial edict, Zezhou is a key point that cannot be lost. "
<s>[INST] Kindly elucidate the central themes in this passage in English: 师至天并关，存节谓诸将曰： 是行也，虽不奉诏旨，然要害之地，不可致失。  [/INST] When the army arrived at Tianjing Pass, Niu Cun-jie told all the generals: "This expedition, although not carrying out an imperial edict, Zezhou is a key point that cannot be lost. "</s>
Kindly elucidate the central themes in this passage in English: 师至天并关，存节谓诸将曰： 是行也，虽不奉诏旨，然要害之地，不可致失。
user
When the army arrived at Tianjing Pass, Niu Cun-jie told all the generals: "This expedition, although not carrying out an imperial edict, Zezhou is a key point that cannot be lost. "
assistant