1)
Why does it say "Ki"?
1.
Malbim: This resolves with above (3), that the Leviyim were counted from the age of 30. Afterwards, David counted them from the age of 20.
2)
Were these David's last words?
1.
Radak: This was [among] his last deeds, to count the Leviyim from the age of 20 and establish them in their Mishmaros.
3)
What is the significance of the number of Leviyim?
1.
'Rashi': David established Mishmaros to be ready for Shlomo [when he will build the Beis ha'Mikdash].
