Why does it say "Mi Amad b'Sod Hashem"?
Rashi: The only ones who can hear what Hashem decreed are those who heed His Torah and Mitzvos, but not these Resha'im.
Radak: Who of them (the false Nevi'im) stood in Hashem's secrets, i.e. Nevu'ah? How can they say that they have His word?!
Malbim: They say 1 that Nevu'ah is impossible, for (a) man cannot know His secrets; (b) one cannot see a prophetic vision or hear His word, for a physical eye and ear cannot perceive or relate to the Creator. (c) Even to hear from afar, e.g. a Bas Kol (voice from Heaven) or a spiritual voice and understand it, is not within man's realm. One who dwells in physicality cannot understand the Divine, which is purely spiritual.
Malbim: They say so to those who deny prophecy. To those who believe in Nevu'ah from Hashem, they say [false] Nevu'os.
What is the meaning of "v'Yere"?
Radak: This is seeing a prophetic vision.
Why is "va'Yishma" repeated?
Rashi: The first truly refers to hearing. The latter is accepting (heeding).