What is swearing "bi'G'on Yakov"?
Radak #1: This is like "Bi Nishbati" (Bereishis 22:16), and Hashem swore "b'Nafsho" (above, 6:8). Hashem is Ge'on Yakov.
Radak #2: Ge'on Yakov is the Beis ha'Mikdash, like "Es Ge'on Yakov Asher Ahav Selah" (Tehilim 47:5). This is like "Mesa'ev Anochi Es Ge'on Yakov" (above, 6:8) - the Beis ha'Mikdash, where the honor dwelled in. Hashem swore in His honor that He made dwell amidst Yakov; with their sins, they removed it from them.
Malbim: He swears in His Kadosh name. The grandeur of Yakov depends on it.
What is the consequence of not forgetting their deeds?
Malbim: Even if I do not punish them immediately, I will not forget; in the end they will receive their punishment.
