What is Bein ha'Mishpatayim?
Radak: It is the herds and pens for flocks.
Malbim: Reuven is on the border. A Gibor on the border must keep the enemy away!
What are Sherikos Adarim?
Rashi: They are voices in war, of the victors and of the vanquished.
Radak: The heard the animals (Malbim - of their many flocks) and sat secure, and were not concerned to come to help Yisrael west of the Yarden.
What is "li'Flagus Reuven Gedolim Chikrei Lev"?
Mahari Kara: This is a great sin, to investigate like this in the heart (to see who will win, and side with him - refer to 5:15:4:1).
Malbim: One need not delve to understand why Reuven did not come to help [like the next verse says].
