1)
What is the meaning of "Zamamti...Leheitiv"?
1.
Malbim: The evil was preparation for good. Via Galus, the land was appeased for its Shabbosos (Shemitos that were not guarded), and their sin was appeased. Now they are prepared for salvation!
2)
What should they not fear?
1.
Radak: Those who prosecute against you - Sanvalat and his colleagues, who intend to cease your work now.
2.
Malbim: Refer to 8:15:1:1.