In the first year of Darius, Daniel was studying the book of Jeremiah’s prophecies when he came upon the prophecy that Israel would be released from captivity after 70 years. The 70th year of exile was coming, and so Daniel began fasting in sackcloth and ashes, and be began confessing the sins of Israel and pleading with the Lord to hear and restore Israel. While he was praying, Gabriel appeared and told him that the Lord had decreed “70 weeks.” Another period of 70 was going to follow the 70 years of exile in Babylon, and, Gabriel told Daniel, at the end of that 70-week period, that period of 70 x 7, the Lord would finally take care of sin. After 70 x 7, the Lord would “finish transgression, make an end of sin, make atonement for iniquity, bring in everlasting righteousness, seal of vision and prophecy, anoint the most holy” (v. 24).
By the time of Jesus, this prophecy was an obsession for many Jews. It told them when the Messiah would come: From the time of Daniel to the Messiah, there would be 70 x 7, 490 years. It told them what the Lord would do: At the end of 70 x 7, the Lord would deals with Israel’s transgressions once and for all. At the end of the 70 x 7 period, there would be a great Jubilee, a release from debt, a manumission of slaves, a return to the land.
Source: Seventy times seven | Peter J. Leithart | First Things