The Jews had disobeyed God’s law of obeying the Sabbath. They had been in the Promised Land for roughly 800 years, and for 490 years, they disobeyed his Sabbath rest. The Sabbath rest was not only every seventh day; it was also every seventh year. The Jews were allowed to work the land for six years, but on the seventh year they had to let the land get a rest. God commanded this because the land needs to recuperate, gaining back its minerals. Also, this was an act of trust and obedience to God. The Jews were trusting God’s provision by not farming for an entire year. Judgment was promised if they disobeyed God’s Sabbath rest:
(Lev. 25:2-4; 26:33-35) Speak to the sons of Israel and say to them, ‘When you come into the land which I shall give you, then the land shall have a sabbath to the LORD. 3‘Six years you shall sow your field, and six years you shall prune your vineyard and gather in its crop, 4but during the seventh year the land shall have a sabbath rest, a sabbath to the LORD; you shall not sow your field nor prune your vineyard… 33‘You, however, I will scatter among the nations and will draw out a sword after you, as your land becomes desolate and your cities become waste. 34‘Then the land will enjoy its sabbaths all the days of the desolation, while you are in your enemies’ land; then the land will rest and enjoy its sabbaths. 35‘All the days of its desolation it will observe the rest which it did not observe on your sabbaths, while you were living on it.
(2 Chron. 36:21) To fulfill the word of the LORD by the mouth of Jeremiah, until the land had enjoyed its sabbaths All the days of its desolation it kept sabbath until seventy years were complete.
God promised the Jews that he would kick them out of the land, if they disobeyed him on this:
(Jer. 25:11-12; 29:10-14) This whole land will be a desolation and a horror, and these nations will serve the king of Babylon seventy years. 12‘Then it will be when seventy years are completed I will punish the king of Babylon and that nation,’ declares the LORD, ‘for their iniquity, and the land of the Chaldeans; and I will make it an everlasting desolation… “For thus says the LORD, ‘When seventy years have been completed for Babylon, I will visit you and fulfill My good word to you, to bring you back to this place. 11‘For I know the plans that I have for you,’ declares the LORD, ‘plans for welfare and not for calamity to give you a future and a hope. 12‘Then you will call upon Me and come and pray to Me, and I will listen to you. 13‘You will seek Me and find Me when you search for Me with all your heart. 14‘I will be found by you,’ declares the LORD, ‘and I will restore your fortunes and will gather you from all the nations and from all the places where I have driven you,’ declares the LORD, ‘and I will bring you back to the place from where I sent you into exile.’
In the book of Jeremiah, God told the people that he would exile them from the land for 70 years, because this was the amount of time that the Sabbath rest had been disobeyed (490 years total). Here in Ezra, we see that this 70 year period had elapsed, as Daniel had also anticipated (Dan. 9:1-2). Ezra records that God moved King Cyrus to let the people back into the land. This was truly a supernatural event. Cyrus even returned the gold and silver that Nebuchadnezzar had sacked from the Temple in 600 B.C. (Dan. 1).
Of course, the length of the exile was set because of their disobedience to the Sabbath, but this wasn’t the primary reason for the exile. The Jews committed idolatry, child sacrifice, and ritual prostitution. This was the reason for being removed from the land.