Why did the vine decline to be king?
It refers to Gid'on. Refer to 8:23:1:1.
Malbim: Also the vine, i.e. a Chacham in civil matters, does not want to abandon his perfection, that he gladdens Hashem and people. I.e. his good Midos bear fruits of Tzedakah, Chesed and mercy, which gladden Hashem, and his good conduct gladdens people. How will he [abandon this to] rule over the trees?!
How does wine gladden Hashem?
Rashi (from Brachos 35a): The Leviyim sing Shirah only over libations [of wine].
Torah ha'Temimah, citing Yerushalmi Sukah 22a: "That gladdens Elokim and people" teaches that only wine proper to gladden people may be offered to Hashem, but not exposed wine, which one may not drink, lest a snake put poison in it.
Radak: Targum Yonasan says that from [the vine] we pour Nesachim in front of Hashem, and it gladdens great 1 people. He distanced Simchah from Hashem, just like he distances other [physical] descriptions from Him, for there is not Simchah or sadness in front of 2 Him. 3 Verses seem to give physical descriptions of Hashem, for the Torah speaks like people do. Also Targum Onkelos of (Bereishis 6:6) "va'Yis'atzev El Libo" is 'He said to break their strength, like His will.' Knowledgeable people understand why this is not done for matters such as "va'Yichar Af Hashem" (Bamidbar 25:3).
Radak: It gladdens great people and Chachamim, and improves their minds (Sanhedrin 70a). Lowly people get drunk, and it befuddles their minds.
I.e. they do not apply to Hashem Himself. "Oz v'Chedvah bi'Mkomo" (Divrei ha'Yamim 1 16:27)! (PF)
Lev Yitzchak: The Targum avoids attributing the same matter to Hashem and people, also above (refer to 9:9:4:3). Targum Onkelos of (Shemos 14:31) "va'Ya'aminu ba'Shem uv'Moshe Avdo" is 'they believed in the word of Hashem and in the prophecy of His servant Moshe.'
Why did Yosam mention three kinds of trees before the Atad?
Radak #1: This was to be brief [and not mention all fruit trees].
Radak #2: He mentioned the three most praiseworthy, and then the lowest, which refers to Avimelech.
Radak citing his father: This corresponding to three matters they said to Gid'on - you should be king, and your son, and your son's son.
