How will Hashem be to him like a father?
'Rashi': This is like it says in Shmuel II, 7:14 - when he acts crookedly, I will chastise him with Shevet Anashim ("va'Yakem Hashem Satan li'Shlomo Es Hadad... Es Rezon ben Elida" - Melachim I, 11:14, 23), like a father rebukes his son. I will not remove My Chesed from him, like I did to Sha'ul and removed his kingship from him. Radak (Shmuel II, 7:14) - 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 (Shmuel II, 7:14): 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 say first say "I will be to him like a father", and then "and he will be to Me like a son"?
Malbim (Shmuel II, 7:14): 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.
In Shmuel II, 7:14, it adds "when he acts crookedly, I will chastise him with Shevet Anashim." Why is this omitted here?
'Rashi': It is omitted here, for it belittles David's honor. (This Sefer is for David's honor.)
Malbim: Afterwards, due to Aveiros, [this Midah ceased;] the Malchus ceased, and Tzidkiyah's eyes were blinded.
Why did He say "I will not remove my Chesed like I removed it..."?
Malbim: In Shmuel II, 7:15, it implies that the Chesed departed from Sha'ul because David was more worthy of the Chesed. Here, Ezra revealed that it departed from Sha'ul because he was not worthy of it, due to his sin.
