Who were Paul's audience?
OT Jews or NT Christians?
If the atonements of the Law were insufficient to save, then no Jew from the post Moses world will go to heaven.
Sinners aren't going there, so the OT had days of atonement.
There is no justification under the Law, but there are atonements.
Incorrect. Christ's sacrifice covers all the OT saints, even Adam and Eve. It doesn't cover wicked people, or enemies of God who know what they are doing. They die the death, the second death from which there is no return.
By the way, Jesus and the apostles were all Jews, that didn't change. Christianity is the fulfillment of Judaism. Christ fulfilled it in the 1st century:
24 "Seventy weeks are determined For your people and for your holy city, To finish the transgression, To make an end of sins, To make reconciliation for iniquity, To bring in everlasting righteousness, To seal up vision and prophecy, And to anoint the Most Holy. (Dan. 9:24 NKJ)
Christ's sacrifice "finished the transgression, made an end of sin, reconciled for iniquity and brought in everlasting righteousness. The promised Messiah came, Jesus Christ, He is the Most Holy that was anointed.
18 "The Spirit of the LORD is upon Me, Because He has anointed Me To preach the gospel to the poor; He has sent Me to heal the brokenhearted, To proclaim liberty to the captives And recovery of sight to the blind, To set at liberty those who are oppressed;
19 To proclaim the acceptable year of the LORD."
20 Then He closed the book, and gave it back to the attendant and sat down. And the eyes of all who were in the synagogue were fixed on Him.
21 And He began to say to them, "Today this Scripture is fulfilled in your hearing." (Lk. 4:18-21 NKJ)
The 70 weeks end during the time of Christ, entering Jerusalem on a donkey is a key event predicted:
4 All this was done that it might be fulfilled which was spoken by the prophet, saying:
5 "Tell the daughter of Zion,`Behold, your King is coming to you, Lowly, and sitting on a donkey, A colt, the foal of a donkey.'"
6 So the disciples went and did as Jesus commanded them.
7 They brought the donkey and the colt, laid their clothes on them, and set Him on them.
8 And a very great multitude spread their clothes on the road; others cut down branches from the trees and spread them on the road.
9 Then the multitudes who went before and those who followed cried out, saying: "Hosanna to the Son of David!`Blessed is He who comes in the name of the LORD!' Hosanna in the highest!"
10 And when He had come into Jerusalem, all the city was moved, saying, "Who is this?"
11 So the multitudes said, "This is Jesus, the prophet from Nazareth of Galilee." (Matt. 21:4-11 NKJ)