What was the sin of your first father?
Rashi: Avraham said "ba'Meh Eda" (Bereishis 15:8).
Radak #1: Adam ha'Rishon [ate from Eitz ha'Da'as]. Sin is in man's nature - "Ki Yetzer Lev ha'Adam Ra mi'Ne'urav" (Bereishis 8:21).
Radak #2: Some say that it is your first king, i.e. Yaravam. Av can refer to a king - "v'Haysah Yad Hashem Bachem uva'Avoseichem" (Shmuel I, 12:15). I say that it is better to say that it refers to Sha'ul, the first king of all of Yisrael.
Malbim: It is the generations at the time of the Mikdash.
Who are "Melitzecha", and what was their sin?
Rashi: Not one of the advocates on whose merit you rely, I did not find sin in him. Yitzchak loved My hater.
Radak: They are your officers and great people. This is like "bi'Mlitzei Sarei Bavel" (Divrei ha'Yamim II, 32:31). The Sarim were proper to rebuke the nation and return them to the good path; they sinned against Me.
Malbim: They are the Kohanim and Nevi'im. Their sins are considered Mezid; the commoners were Shogeg, and their Mezid sins are considered Shogeg.
