About what was the Bris?
Rashi: Guard My Torah. Radak - it was with your fathers, but it is as if I made the Bris with you - "Lo Es Avoseinu Karas Hashem Es ha'Bris ha'Zos Ki Itanu" (Devarim 5:3).
What is the meaning of "v'Ruchi Omedes b'Sochechem Al Tira'u"?
Rashi: [If you will guard My Torah,] My Ru'ach will dwell on your Nevi'im, and you will not fear.
Radak: This refers to Ru'ach ha'Kodesh. However, after they sinned and did not do Torah and Mitzvos, Ru'ach ha'Kodesh and Nevu'ah ceased, in the days of Zecharyah and Malachi.
Radak citing Targum Yonasan: My Ru'ach stands amidst you, and My Nevi'im teach among you.
Malbim: Even though the Ru'ach is not aroused to do open miracles and wonders, and it does not go among you, it stands among you, and is ready to act.
