1)
Who are "Achai v'Re'ai"?
1.
Rashi: Yisrael (are David's brothers and friends).
2.
Radak: Bnei Galus say so about each other.
2)
What will he speak?
1.
Rashi: David will speak Shalom [of Yerushalayim]. Radak - that the exiles will return to it.
