How could Barak say that he will go only if she does? One who transgresses a Navi's words is Chayav Misah! Also, she already told him that he will win!
Malbim: He said, if you will not come, people will not agree to fight, so there is no point for me to try. R. Yehudah (in Bereishis Rabah 40:4) - if you will go with me to Kedesh (to recruit soldiers), I will go with you to Chatzor 1 . R. Nechemyah - if you will go with me to Shirah, I will go to the war.
Yefe To'ar - the text should say 'Tavor'.
Yefe To'ar: To help me to sing, or to compose a Shirah over the victory, with your Ru'ach ha'Kodesh. (How did he know that there would be a Shirah? There was no Shirah for the salvations of Osni'el and Ehud! Perhaps he understood that this is a greater salvation due to Sisera's great army. Or, he recognized the need for Shirah. Hashem wanted to make Chizkiyah Mashi'ach, but it was blocked because he did not sing Shirah over the miracles (Sanhedrin 94a). (PF)
How does this answer the question? Even if he estimates that he will not succeed, she commanded him to try! (PF)
