How will Hashem be to him like a father?
Radak: I will rebuke him for his sin like a father rebukes his son, and I will not remove my Chesed from him, like I did to Sha'ul and removed his kingship from him. Rather, the kingship will be to his descendants forever. This refers to David's descendants, not only Shlomo, rather, also Rechav'am and his descendants.
Malbim: He oversees him, and when the son begins to make his path crooked, immediately he rebukes him and returns him to the good path. He does not allow him to falter so that his Emunah will depart. Malchus Beis David is founded on Emunah and Chesed.
Why does it first say "I will be to him like a father", and then "and he will be to Me like a son"?
Malbim: When one serves Hashem amidst love, he is like a son based on his deeds. When he ceases to do so, he is like a slave who rebelled against his master. Hashem will act like a father before he acts like a son. I will not let him reach serious sins that require cruel punishment; I will always be like a father to him.
What is "Shevet Anashim"?
Rashi: It is Hadad and Rezon ben Elida. 1
Radak: It is like people afflict their children with a staff
Malbim: It is a staff used to hit people, not one used to hit a horse.
Radak: "Va'Yakem Hashem Satan li'Shlomo Es Hadad", "va'Yakem Elokim Lo Satan Es Rezon ben Elida" (Melachim I, 11:14, 23).
What are "Nig'ei Bnei Adam"?
Rashi: This is Ashmedai (king of the demons), who removed Shlomo from his kingship. Demons are called Bnei Adam ha'Rishon, for all 130 years that Adam separated from his wife, Ruchos were heated and gave birth due to him (Tanchuma Bereishis 23).
Radak: One strikes his son with a staff in a way that will not kill him - "Ki Sakenu va'Shevet Lo Yamus", "v'El Hamiso Al Tisa Nafshecha" (Mishlei 23:13, 19:18).
Malbim: They apply to people naturally. 1
Malbim: "U'Fakadti v'Shevet Pish'am uvi'Nega'im Avonam" - for Pesha (rebellion) He afflicts with a staff, and for Avon, i.e. denial and crookedness of intellect, He afflicts with Nega'im that cling to his body. The latter sins are more internal, for the intellect is the person himself.
