Why does it say "Kol Yisrael"?
Malbim: Had he changed to say like the elders, the astute in the nation would have realized that he schemes, and he will return to rule harshly over them, but most would not have realized this, and been pleased with his words. Now, all saw that he did not heed them.
What is the meaning of "Mah Lanu Chelek b'David"?
Radak: It is a question - what do we still have in him, since [Rechav'am] does not hear our voice and says that he will make our yoke heavier. Who forces us to have a share in him?! They mentioned David, for he was first; also his son or grandson is called David. The same applies to "v'David Avdi Nasi Lahem l'Olam" (Yechezkel 37:25).
Radak citing Targum Yonasan: We do not have a share in David.
Malbim: There are two reasons for a nation to choose a king from a house. (a) Kingship was from this house from of yore. (b) They will benefit from the one whom they want to make king. Corresponding to this, they said 'we have no share in David', for he is not from our Shevet.
Why did they add "v'Lo Nachalah b'Ven Yishai"?
Malbim: Refer to 12:16:2:3. Yishai was a commoner. Therefore, [Rechav'am's] kingship depends on our approval.
Why did they say "l'Ohalecha Yisrael"?
Rashi (Hoshe'a 3:5, from Yalkut Shimoni Shmuel I, 106): We read this like lei'Lohecha (your gods). Yisrael despised three things in the days of Rechav'am - Malchus Shamayim, Malchus Beis David and the Beis ha'Mikdash.
Chomas Anach: Our Batei Kenesiyos and Batei Midrash, which are called Ohalim, will suffice for us (we do not need the Beis ha'Mikdash).
Why did they say "Re'eh Beischa David"?
Rashi: The Beis ha'Mikdash that you built, it is only for you. 1 Panim Yafos (Devarim 12:5) - Dushnah Shel (a place outside) Yericho was designated in lieu of the place where the Mikdash will be built [the owner of that place will receive Dushnah Shel Yericho]. Yericho was in Galil, in the Malchus of Yaravam. Since he fought with Rechav'am, surely he did not give to him Dushnah Shel Yericho. If so, the place of the Mikdash is only of Yehudah 2 .
Radak: Who remains with you? Over whom will you rule?!
Radak citing Targum Yonasan: Rule over the people of your house, David.
Malbim: Beis David was built from the tents of Yisrael. They abandoned their tents and built his house. If they will return to their tents, he has no house!
Panim Yafos: This explains also why in Yehoshua (22:24-25), there was concern only lest Yisrael say to Bnei Gad and Bnei Reuven "you have no share in Hashem", but not to Chetzi Menasheh, for Menasheh had a share in Dushnah Shel Yericho, [so they will have a share in the Beis ha'Mikdash when it is built. Gad and Reuven forfeited their share in everything west of the Yarden, including Dushnah Shel Yericho, so they will not have a share in the Mikdash. This is astounding, that already Yisrael know that Yaravam will fight with Rechav'am and not give Dushnah Shel Yericho. If this was important to them, they could have stipulated to accept a king only if he will let Yehudah keep Dushnah Shel Yericho, so Yisrael will retain a share of the Mikdash! - PF]
