Why did Hashem mention what happened beforehand?
Malbim: I took them from Egypt, from being under the Ma'arachah (influence of the stars) to the shade of Hashgachah, and they abandoned Me to serve idolatry, for they prefer being under ministers and stars. Also, you conducted them based on miraculous Hashgachah, and they prefer nature, to trust in human strength. This is the intent of the opinion that they wanted to serve idolatry (refer to 8:6:1:2). 1
Especially according to Ramban (Vayikra 18:25), who says that the angels appointed over the 70 nations are idolatries.
Why did Hashem say "Gam Lecha"?
Radak: This is like "Gam Imach." You went out in front of them in their wars, and succeeded to the point that their enemies made peace with them. They did not need war, for you returned them to the good path. Even so, they rebelled against Me and you to request a king, which they did not need, for their only war was with Nachash Melech Amon (Perek 11). 1
Malbim: Refer to 8:8:1:1.
The verses imply that Nachash threatened Yisrael only after Shmuel anointed Sha'ul. (PF)
