Rashi: If you come to fight against the Satan, come with strategies - Teshuvah, Tefilah and fasting.

R. Yonah: It is proper to think before acting. He should take counsel about his intent with others. Then his intent will be established, proper and succeed. One should not rely on a matter without prior thought. This is like Chazal said, [even if] you have 60 advisors, do not abandon the counsel of your Nefesh ¹ . One should toil to think about his deeds more than others toil to investigate them. However, he should test his intent with others' counsel - man's Sechel is limited. Perhaps he erred and overlooked something. They will make him understand his mistake. Also, often one's desire closes the eyes of Sechel; others will inform him.

Malbim: I explained above (11:14) that Machashavah thinks about all possibilities. It is like a flow of flooding water. When he decides to do like one possibility based on the desired goal, this is called Etzah. Then he has a base for his thoughts, and they do not float on the wings of Ru'ach. Our verse teaches that one must decide on one Etzah.

R. Yonah: War requires thought, counsel and strategies to see what will result. He must think, if the enemies will do such, how he can outsmart them. He will prepare the way how so we will have ability to overcome them. Therefore, do not make war without Nevonim who know strategies.

Malbim: War requires Tachbulos - binds of many Etzos. Also his enemy has Etzos. He ties rope to rope, causes and effects, so whatever the enemy does, there is counsel against it.

Malbim: I explained above (14:2) that for war, it is good to have many counselors; to give several Etzos, for all possible ways that the enemy might turn. I explained "Hafer Machashavos b'Ein Sod uv'Rov Yo'atzim Takum" (15:22) that if one does not keep the Etzah secret, he will not achieve his goal. Then he also needs many advisors to counsel what to do if the Etzah is annulled via revelation of the secret.