Can you refer to the chapter where you understood that some of the believing Jews were falling back to the temple rituals.
We know there were thousands of Jews who accepted Christ as the Messiah, but still held to the law of Moses.
When Paul came to Jerusalem to see the brethren, the Judaizers laid in wait to kill him because Paul spoke against the law of Moses.
Acts 21:20-21
"And when they heard it, they glorified the Lord, and said unto him, Thou seest, brother, how many thousands of Jews there are which believe; and they are all zealous of the law:
And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to forsake Moses, saying that they ought not to circumcise their children, neither to walk after the customs."
Now I ask you, is there a gospel for the Jew and another for the Gentile. NO, there is not. This is the framework of the book of Hebrews. A new and better covenant with better promises.
The Christian Jews were being persecuted by the Judaizers because of the law of Moses that Paul said the Christian gentiles were not to do. They hounded Paul throughout his entire ministry holding to the law. In fear of the Judaizers, the Christian Jews were turning back.
Paul compares the priest of the old covenant to the priest of the new covenant, the animal sacrifices to the sacrifice of Christ. Paul is telling the Christian Jews that Christ has met the demands of the law and He Himself is now the High Priest and Mediator. He tells them that if the first covenant had been sufficient, there would be no need for a second. Remember that Paul is speaking to the Jews who have accepted Christ.
He warns them against letting the New Testament slip away (2:1-4), against hardening the heart against the Holy Spirit (3:7-19) against falling away (5:11-6:12), against committing the willful sin of treading underfoot the Son of God, counting His Blood as common Blood, and doing insult to the Holy Spirit (10:26-29), all this being involved in the act of renouncing professed faith in Christ and returning to the Levitical sacrifices.