1)
What is the meaning of "Shoresh l'Matah"?
1.
Radak (Melachim II, 19:30 citing Targum Yonasan): Like a tree that sends its roots down, and lifts its foliage above.
2)
What does the verse teach?
1.
Malbim: All will increase - the fortified cities, the kingship and the common people.
