1)
What does the vine represent?
1.
Bereishis Rabsi (20:15) It represents Gid'on, who offered to Hashem, just like we offer Nesachim from the vine to Hashem.
2.
Rashi: It refers to Gid'on from Yosef, about whom it says (Bereishis 49:22) "Ben Pores Yosef"; the Targum is 'k'Gofen di'Ntziv..."
3.
Malbim: This alludes to someone intermediate between good and pleasant, i.e. beneficial. The vine gladdens people (Tehilim 104:15), makes them astute (Yoma 76b) and heals (Bava Basra 58b). I.e. they should pick a Chacham in civil matters with good Midos who will guide them in the righteous path and proper judgment.
