Does he deny Hashem?
Radak: No. It says "Negdecha" - he knows that Hashem knows us and our deeds! Rather, one who denies to his colleague, it is as if he denies Hashem - "u'Ma'alah Ma'al ba'Shem v'Chichesh ba'Amiso" (Vayikra 5:21). Since he deposited with him or lent to him without witnesses, Hashem was the witness, and he contradicts Him.
Radak based on Targum Yonasan: He contradicts Hashem's word, i.e. His Mitzvah not to deny or lie to a colleague.
Malbim: Yes. He rebelled against Him and denied Him.
What is the significance of "v'Nasog me'Achar Elokeinu"?
Radak: This is the opposite of "Acharei Hashem Elokeichem Telechu" (Devarim 13:5). Also Nasog, Daber, Horo v'Hogo are Makor. The root of Nasog is Nasag, being late, like one who turns back. Alternatively, the Nun in Nasog is for the Nifal conjugation; it is not from the root. It is like "Lo Nasog Achor Libenu" (Tehilim 44:19).
Malbim: Hashem alludes to the Creator. Elokeinu alludes to His Hashgachah over us, and reward and punishment. They deny also these. Normally, at the least a sinner fears Hashem's punishments.
What is "Daber Oshek"?
Rashi: This is like Ledaber Oshek (to speak oppression).
Malbim: This explains "v'Chatoseinu Ansah Banu" (12) - sins Bein Adam l'Chavero. They openly stole and oppressed and glorified themselves about this, and testified and told about it. When he was not able to steal or kill, he made up a story that he did so! Refer to 59:13:5:6.
What is "Sarah"?
Radak 1 : It is something crooked.
In some editions this mistakenly appears in his Perush on verse 14.
What is the meaning of "Horo v'Hogo [mi'Lev Divrei Sheker]"?
Rashi #1: To shoot and take out. Horo is an expression of "Yarah va'Yam" (Shemos 15:4).
Rashi #2: The Rav and the Talmid. V'Hogo is like "Hogah Min ha'Mesilah" (Shmuel II, 20:13), "Hago Sigim mi'Kasef" (Mishlei 25:4).
Radak 1 : Horo is like "Haro Amal" (4), like I explained above (the verse depicts intent as pregnancy); they carry out their thoughts to speech and deed [of sin, i.e. birth]. Their words are Sheker. Here the Hei has a Cholem; normally, it has a Kamatz. The same applies to v'Hogo; the root is Hagah.
Radak citing his father: Horo is like "u'Lehoros Es Bnei Yisrael" (Vayikra 10:11).
Radak citing Targum Yonasan: They take out [words of Sheker from their hearts].
Malbim: They needed to concoct Sheker from their hearts to glorify themselves about oppression, for it was so dear in their eyes.
In some editions this mistakenly appears in his Perush on verse 14.
