What is the meaning of "va'Ya'ad Hashem"?
Rashi: He warned them 1 [Radak - via witnesses. This is Hifil. This is like "Ha'ed He'id Banu ha'Ish" (Bereishis 43:3), "Ha'idosi Vachem ha'Yom" (Devarim 4:26).]
Malbim: This was in the days of Eliyahu and Elisha, via many Nevi'im. He warned about the punishments that will come on them.
Why is "Nevi'ei" written with a Vov at the end?
Radak: This refers to one who was His Navi, and not the false Nevi'im.
Radak citing Eichah Rabah 2:14: Hashem sent a Navi in the morning, and a [different] Navi in the evening.
What are "Nevi'ei Chol Chozeh"?
Rashi: They are prophets of every [prophetic] vision. Chozeh can be a noun, like "v'Im She'ol Asinu Chozeh" (Yeshayah 28:15).
Radak: This is like Nevi'im Chol Chozeh (prophets, every seer). Also "Chalonei Shekufim" (Melachim I, 6:4) is like Chalonim Shekufim. "Anshei Mechukah" (Yechezkel 23:4) is like Anashim Mechukah. He warned via every Navi and seer.