1)
How do they help each other?
1.
Rashi: They 1 help with Brachos, e.g. "Baruch Avram" (Bereishis 14:19) and with gifts, e.g. "va'Yiten Lo Ma'aser mi'Kol" (ibid., 20).
2)
Why does it mention Re'ehu and Achiv?
1.
Radak: The matter is repeated in different words; it is as if it says v'Ish El Achiv.
3)
For what do they strengthen each other?
1.
Rashi: For war. [They hope that] perhaps their gods will stand for them.
2.
Malbim: (For war.) They say, do not rely on the help - rather, be valiant!
