1)
Why is "Cholek Im Ganav Sonei Nafsho"?
1.
Malbim: Even though he himself did not steal, only he divides with the thief, since he knows about the theft and does not testify, he hates his own Nefesh (refer to 29:24:2:1).
2)
What is the significance of "Alah Yishma v'Lo Yagid"?
1.
Rashi: They impose an oath on him 'if you saw that Ploni stole such and such from me [come to testify for me]', and since [the witness] shares the theft with Ploni, he does not testify. Malbim - with the oath is a Cherem that anyone who knows must testify. When he does not testify, the curse takes effect on him.
