Why does it say that you will return "bEi'lokecha"?
Rashi: In trust and reliance on Him. He is your security on whom you can rely, and you will return to Him.
Radak #1: You, Zera Yakov, if you desire Elokecha, Tashuv i.e. rest. This is like "b'Shuvah va'Nachas Tivashe'un" (Yeshayah 30:15).
Radak #2: The prefix Beis is like Lamed. Tashuv is Teshuvah. Also "v'Shilach Es ha'Sa'ir ba'Midbar" (Vayikra 16:22) is like l'Midbar. "Ranenu Tzadikim ba'Shem" (Tehilim 33:1) is like la'Shem.
Radak citing Targum Yonasan: You will strengthen yourself in Avodas Elokecha.
Malbim: The condition to return to your level is via your G-d - Elokei Yisrael, not via an angel.
What is the significance of "Chesed u'Mishpat Shemor"?
Rashi: If you guard Chesed and Mishpat, you are assured to hope to His salvation constantly.
Radak: On condition that you guard Chesed and Mishpat, you can rest and not fear the enemy. These are Hashem's Midos - "Ki Ani Hashem Oseh Chesed Mishpat u'Tzedakah ba'Aretz Ki v'Eleh Chafatzti Ne'um Hashem" (Yirmeyah 9:23). Even though here it does not mention Tzedakah, elsewhere it says "Shimru Mishpat va'Asu Tzedakah" (Yeshayah 56:1). Also, it says here "v'Kave El Elokecha Tamid."
What do we learn from "v'Kave El Elokecha Tamid"?
Refer to 12:7:2:1.
Radak: This is Tzedakah and straightness, to hope constantly to Hashem. Even if you have great good, wealth and property, say that it is from Him; remember Him constantly and hope to Him - "v'Zacharta Es Hashem Elokecha Ki Hu ha'Nosen Lecha Ko'ach La'asos Chayil" (Devarim 8:18). This is unlike Efrayim, which said "Ach Asharti Matzasi On Li" (below, 9).
Malbim: Hope to Hashem, and not to an angel or Sar.
