Why does it say "va'Ytzav ha'Melech"?
Malbim: This hints that he fulfilled the command of his father "Yadata Es Asher Ta'aseh Lo" (verse 9).
Why does it say "va'Yetzei"?
Radak: Benayahu went out from in front of the king and took Shim'i to the place of Mishpat, and killed him there.
Why does it say that the kingship was solidified in his hand?
Rashi: Shlomo was not punished for all of these (killing Adoniyahu, Yo'av and Shim'i, and deposing Evyasar).
Radak: All his enemies died.
Malbim: This shows that until now, there was opposition. Yo'av and Evyasar plotted evil via Adoniyahu, and Shim'i sowed evil via Bnei Binyamin. Now that they were dead, the kingship was solidified.
It already said (verse 12) that his kingship was very solid!
Malbim: Above it said Meluchah, i.e. from the aspect of the king. Here it says ha'Mamlachah, from the aspect of the state. In the state there were still objectors; only now there was no opposition.
