1)
Which Bris did He remember?
1.
Ibn Ezra: It is "Bris Rishonim" (Vayikra 26:45) of Sinai, which Hashem made with the Rishonim, i.e. those who left Egypt. 1
2.
Radak: It refers to His Bris with the Avos.
1
Ibn Ezra: It is not the Bris that He made with the Avos, for verse 42 there already mentioned that. (What is the source that here refers to Bris Rishonim? If it is because Zechirah is written with it, it is written also with Bris Avos - "va'Ezkor Es Brisi" (Shemos 6:5)! - PF)
2)
What caused Him to remember His Bris?
1.
Rashi: They repented.
