1)
What is the meaning of "Ya'arimu Sod"?
1.
Radak: They take counsel with each other with schemes to come against us.
2)
Who are "Tzefunecha"?
1.
Radak: They are Yisrael; they are Tzefunim (hidden) in Your hiding place - "Titzpenem b'Sukah Meriv Leshonos" (31:21).
2.
Malbim: [They enemies oppose] hidden matters of Elokus, e.g. Emunah in Hashem's unity, and the connection of Your Elokus and Your Hashgachah over Yisrael. They also want to nullify from Yisrael the Torah and Mitzvos that You gave to them.
