ושב ה' את שבותך, “the Lord will return with you from your captivity;” in chapter29,27, G-d had been described as expelling His people from the Holy Land to any other land, now, if the people have repented their wrongdoings, He promises to bring them back and remain with them.

כאשר שש על אבותיך, ”as He used to take delight in your forefathers.” This is a reference to the generation who inherited the Holy Land. G-d is addressing the exiles at this point.

כי תשמע בקול...כי תשוב, “if you will listen to the voice of Hashem.....and return to the Lord;” we learn here that the time for the redemption from exile depends on two factors, a) penitence, b) performance of the positive commandments and avoiding the transgressions listed in the negative commandments.

הכתובה, “which has been recorded in writing; we would have expected this word to be in the plural mode as it covers multiple laws. Instead we find a singular feminine mode. This is not something unique; for instance we find something analogous in Exodus 17,12 where Moses’ hands are described as remaining steady, i.e. ויהי ידיו אמונה.

ולא מעבר לים היא, “neither is it beyond the ocean;” this refers to the Mediterranean, which man cannot cross (as even if he had a ship) because the surface of the waters are dark (and he would get lost at night). (Ibn Ezra).

העידותי בכם היום את השמים ואת הארץ, “I call as witness against you this day both heaven and earth;” witness in the positive as well as in the negative sense of the word. If you will perform the commandments in the Torah heaven and earth will testify on your behalf; if not, they will testify at the heavenly tribunal against you. They will do this by heaven denying the essential rain to make your crops ripen. (Deut. 11,17)

כי הוא חייך, “for He is your life;” a reference to Hashem.