Why did he say "v'Hikaftem Al ha'Melech"?
Malbim: Here he addresses those who guard inside. They literally surrounded the king.
Who is "ha'Ba El ha'Sederos"?
Rashi: It is a stranger who comes to the place called Sederos, the place where the king goes from his house to Beis Hashem. I do not understand the expression Sederos.
Radak citing Targum Yonasan: It is inside the order of your Mishmaros (where you guard). In Divrei ha'Yamim II, 23:7 it says "veha'Ba El ha'Bayis." This is the same, for they guarded the entire Bayis - "mi'Kesef ha'Bayis ha'Ymanis Ad Kesef ha'Bayis ha'Smalis la'Mizbe'ach vela'Bayis" (verse 11).
Malbim: It is one who comes to where the guarding begins outside.
Here it says that they will be with the king when he leaves and enters. Why does it say in Divrei ha'Yamim II, 23:7 when he enters and leaves?
Malbim: There it discusses those guarding from the outside. Here it discusses those guarding from the inside.