Rashi (from Vayikra Rabah 7:1): This hatred was repressed in front of Hashem for almost 900 years, from when they were in Egypt until Yechezkel. His love covered up for them. Since they sinned greatly now, [the hatred] was aroused - "Sin'ah Te'orer Medanim" (Mishlei 10:12).

Radak: The rebuke began when they became a nation in Egypt. He chose them on the day that He sent to them His Nevi'im - Moshe, Aharon and Miryam. We find that they rebuked them only from Yechezkel.

Malbim: There were two matters in the choice of Yisrael in Egypt. (a) He chose them because they are Yisrael - attributes in their Nefashos that are worthy of Divine matters. (b) Refer to 20:5:2:2.

Radak: This is like it says "Asher Nasasi Es Yadi Lases Osah l'Avraham l'Yitzchak ul'Yakov" (Shemos 6:8). Here it explains that it was given to Avraham and Yitzchak for the sake of Zera Yakov. And so it says there "v'Nasati Osah Lachem ¹ Morashah Ani Hashem" (ibid.)

Malbim: He chose Yisrael also because they are the seed of Beis Yakov, and the Bris of the Avos. He raised His hand to fulfill His Shevu'ah to the Avos.

Radak: I became known to them via My Nevi'im that I sent to them.

Malbim: He revealed to them the Divine matter.

Radak: This is a Shevu'ah. Also Yonason translates so.

Malbim: I am already Elokeichem - I am tied with you in the Bris of old, to be Elokim to you.