What did Jeremiah prophesy about the land enjoying its Sabbath rest?
Jeremiah foretold that the land would enjoy her Sabbaths for as long as she lay desolate, keeping Sabbath until three score and ten years—70 years—were fulfilled. This meant the land would receive the rest Israel had denied it by not letting the farmland lie fallow every seventh year.
Les explains that Jeremiah had foretold the land would enjoy her Sabbaths as long as it lay desolate; it kept Sabbath to fulfill the 70 years. This was certain because when God prophesies, especially within a time frame, it will happen. The context is the Babylonian captivity: Nebuchadnezzar carried those who escaped the sword to Babylon, where they served him and his sons until the kingdom of Persia. God had required Israel to let the farmland lie fallow every seventh year—a sabbatical year—but Israel's greed led them to ignore it, so the land received its missed Sabbaths during the desolation.
To fulfil the word of the LORD by the mouth of Jeremiah, until the land had enjoyed her sabbaths: for as long as she lay desolate she kept sabbath, to fulfil threescore and ten years.