Who is "Ed Kezavim"?
R. Yonah: He normally testifies about Kezev when he tells matters - "Yafi'ach Kezavim" (14:5). The class of liars is among the most corrupt groups.
Malbim: It already said "v'Yafi'ach Kezavim Lo Yimalet", "v'Yafi'ach Kezavim Yoved" (19:5, 9). Each place is explained according to the context. Here it discusses the tradition from generation to generation until the head of Even Yisrael regarding Mitzvos, Emunos and De'os. Sometimes someone testifies about something that he did not hear, and he wants people to receive a false tradition, whether in Mitzvos, Emunos or De'os. The verse says that he will perish. Hashem's Hashgachah will cause Emes to last and Sheker will be finished like smoke.
Who is "Ish Shome'a"?
Rashi: He accepted the Torah's Mitzvah "Lo Sa'aneh v'Re'acha Ed Sheker" (Shemos 20:13).
R. Yonah: Understanding is called Shemi'ah - "Goy Asher Lo Sishma Leshono" (Devarim 28:49) - because full hearing is understanding what he hears. Ish Shome'a understands what he hears and is precise to retell it. He stores it in his heart without addition or detraction. A support for this is that it is put opposite "Ed Kezavim."
Orchos Tzadikim (Sha'ar ha'Sheker): He puts his heart to hear and understand the matter and words that were told in the way of Emes. There is no Sheker in his mouth.
Malbim: One who says a matter that he heard, his tradition will last forever.
Why will he speak forever?
R. Yonah: Even though it is not a good Midah to speak a lot - "b'Rov Devarim Lo Yechdal Pesha" (10:19), one who is meticulous to hear accurately, and retell without addition or detraction, he may speak the entire day. However, he must understand that they are matters proper to tell them.
Orchos Tzadikim (Sha'ar ha'Sheker): [Because there is no Sheker in his mouth,] people want to hear his words. They will not rebuke him for them.
Malbim: If he will testify about true matters that were received, that he heard from ancient mountains, they will be fulfilled forever.
