1)
Why did Rechav'am abandon Torah when his kingship strengthened?
1.
Malbim: He did not serve Hashem l'Shem Shamayim, rather, so his kingship would be secure against Yaravam, who served calves. Therefore, after he built fortified cities, and many came to his kingdom from Yisrael, he did not fear Yaravam, he abandoned Torah.
2)
Why did Yisrael abandon Torah together with Rechav'am?
1.
Malbim: They guarded Torah only due to the king's command.
