until the land was appeased for its Sabbaths Because prior to that, the land was not appeased for its Sabbaths.

all the days of its desolation it rested until the completion of seventy years [corresponding to] the Sabbatical and Jubilee years that Israel had neglected to observe in the land, and corresponding to them they were exiled for seventy years. The land of Israel rested for those seventy years. The Israelites provoked [God] in their land for 430 years. These included 390 years from the time they entered the land until the ten tribes were exiled therefrom, and they are explained (as follows): 243 years from the time Jeroboam ascended the throne until Hoshea the son of Elah was exiled, and 111 years during the administration of the judges, when they provoked [Him], and the rest are obscure. That is what is stated in Ezekiel (4:4ff.): "And you shall lie on your left side, and you shall place the iniquity of the house of Israel, etc., 390 days, etc. And when you complete these, you shall lie on your right a second time, and you shall bear the iniquity of the house of Judah, 40 days, a day for a year, a day for a year.⁠" This teaches that the house of Judah sinned from the time that the ten tribes were exiled until Jerusalem was destroyed, for 40 years. How so? Twenty-two years of Manasseh, as it is written (II Kings 21:3): "according to all that Ahab did,⁠" and Ahab reigned 22 years (and he [Manasseh] repented for thirty-three years, totaling fifty-five years.) Add 2 years of Amon, and 11 of Jehoiakim, totaling thirty-five years, and this prophecy was transmitted to Ezekiel in the 5th year of Zedekiah, totaling 40 years. The sum total of them all, of both Israel and Judah, is 430 years. Note that there are 64 Sabbatical and Jubilee years in 400 years. There are 5 Sabbatical years in 35 years, totaling 69, and the last Jubilee year was counted for them as iniquity, for because of their iniquity they were exiled therefrom. Hence the 70 hallowed years of Shemittah that Israel did not observe. They were consequently exiled for seventy years to fulfill what was said, (Lev. 26:34): "Then the land will be appeased regarding its Sabbaths.⁠" So it is explained in Seder Olam (see ch. 26). Chronicles is concluded with this since he says: "until the completion of seventy years.⁠" He had to state these verses and those of Ezra (in the beginning) to let us know that when those seventy years were over, "the wheel rotated" and they returned to their land. He therefore said here: "in the first year of Cyrus, the king of Persia" until "Who among you is of all His people, etc., and he may ascend.⁠" The reason that the "vav" [and] of "And in the first year" is added, is because the Book of Daniel intervenes, for the book of Ezra continues in sequence after the Book of Daniel, and this "vav" connects them together.⁠"