"the son of your mother" — your brother from your mother.
"or your son" — in any event (i.e., even if he is a mamzer).
"who is as your soul" — your father and your mother.
"in secret, saying": We are hereby taught they utter their words (of incitement) only in secret, as it is written (Proverbs 7:9) "In the evening, in the close of day, in the midst of night and darkness." But words of Torah are uttered only in the open, as it is written (Ibid. 1:20) "Wisdom (Torah) sings in the streets, etc."
(Devarim, Ibid.) "Let us go and serve other gods, whom you did not know, you, nor your fathers": R. Yossi Haglili says: This is in denigration of Israel. For the idolators do not forsake what their fathers have bequeathed to them, but Israel (are amenable to) forsaking what their fathers have bequeathed to them to go and serve idolatry.