These “weeks” are weeks of years (Gen. 29:27; Lev. 25:40). So Gabriel is telling Daniel, “It will be 490 years until something happens to your people (Israel) and your city (Jerusalem).”
Then God will “finish the transgression.” Transgressions are sins, but sins against a specific law (Rom. 4:15). The transgression is the same one Isaiah spoke about (53:8). The Lord died for all their transgressions, of course (v. 5), so the transgression must be the same one Isaiah said would cause the earth to fall and not rise from (24:20). Since the earth will fall due to all her transgressions, Isaiah is summing up their transgressions as the transgression. That means Gabriel is saying God will make an end of the sum total of all transgressions. He’ll make an “end of sins” of any kind as well (Dan. 9:24).
But to do that, God will have to “make reconciliation for iniquity” first. We need reconciliation because our sins separated us from Him when Adam fell (cf. Isa. 59:2). But to make it, someone had to atone for it. Israel’s priests made reconciliation with animals (II Chron. 29:23, 24) which were a type of the ultimate atonement Christ made (Rom. 5:11).
Paul says we have His atonement “now,” but the nation of Israel didn’t, so they had a “day of atonement” every year (Lev. 25:9). But just as their feast of passover was a type of the ultimate passover (I Cor. 5:7), their day of atonement was a type of an ultimate one. And just like the typical feast of day of atonement, it’ll come right after the feast of trumpets (Lev. 23:23-27). The ultimate feast of trumpets will gather saved Jews into the kingdom (Mt. 24:31), and that’s when they’ll get their ultimate day of atonement (Rom. 11:26, 27).
Individual Jews were saved and had their sins atoned for (John 5:24; I Jo. 3:15, etc.) but they were part of “the commonwealth of Israel” (Eph. 2:12), so they needed an ultimate day of atonement as a nation. And when that day comes, Gabriel says God will bring in the “everlasting righteousness” of the kingdom of heaven on earth.
That’s when God will “seal up the vision and prophecy.” When Daniel was finished describing his visions about the kingdom in the book of Daniel, God told him to seal the book (12:9). But when the kingdom he wrote about actually comes, all the visions about the kingdom will also be sealed up. It almost happened 2,000 years ago (Mt. 4:17; Acts 3:24) but was interrupted by the mystery.
When it finally comes, God will “anoint the most holy,” i.e. the most holy place (Ex. 26:34). Anointing was done with oil, a type of the Spirit (I Sam. 16:13). When the temple is rebuilt in the kingdom, God will anoint it with His Spirit.
“Seventy” years wasn’t a number God picked out of a hat. Israel’s history is divided up into four 490-year sections. Daniel was standing at the end of the third one, and when he learned he was about to be released from captivity and allowed to return to Israel, he thought the kingdom would start. God sent Gabriel to tell him that it would be another 490 years until the kingdom.
First he was told it would take 7 weeks to rebuild Jerusalem (Dan. 9:25), and then 62 more weeks until Messiah. He was told to start counting the weeks of years when the command went forth to built the city (Neh. 2:1-8), not from the command to build the temple (Ezra 1:2, 3). This works out to the day when the Lord rode the donkey into Jerusalem.
It works out if you don’t use our 365-days-a-year calendar, that is! God taught the Jews to use a 360-days-a-year calendar with each month having 30 days (Compare Gen. 7:11, 12, 24; 8:3, 4 and see Rev. 11:2, 3). It’s why the Lord spoke to the Jews about “this thy day” on that day (Lu. 19:42).
This is how the wise men knew it was time for Messiah to be born. They knew that He’d be a priest (Zech. 6:13), and priests had to be 30 (Num. 4:1-3), so when they saw Balaam’s star (Num. 24:17) they compared Daniel 9’s timetable for His presentation to Israel and subtracted 30 years and knew it was time for His birth within 3 years.
Only the true God could have made a prophecy like this!