What is the meaning of "Rach u'Mashu'ach"?
Rashi citing Targum Yonasan: I am a commoner and elevated to be king.
Radak: I am soft in kingship, as if I was anointed today, for today was the first day of his kingship over Yisrael, via Avner, and Bnei Tzeruyah are harsher than me. They confound my kingship.
Radak citing Bava Basra 4a: Rach is an expression of kingship 1 ; we learn from here.
Also Rashi (Bereishis 41:43) says so about "Avrech"; refer to 41:43:2:1 and the note there.
Why did he call them Bnei Tzeruyah, and not by their father's name?
Radak: Even though their mother is my sister 1 , and they should have been concerned for me, they were not. Elsewhere they are called Bnei Tzeruyah, for this is more honorable for them, due to [her connection to] David.
Tzeruyah was the daughter of Nachash (17:25), i.e. Yishai.
Why did David ask Hashem to punish them?
Malbim: Since he could not punish him through people, he was allowed to ask Hashem to do so.
