So we are still under the ENTIRE Law of Moses? We need to be careful not to confuse His teachings that apply to Jews under the Old Covenant and His teachings that apply to the Church, under the New Covenant. If we don't, then the Old Covenant ends up getting intermingled with the New Covenant.
I think you miss his point. He isn't "Saying" anything, he is simply quoting our savior on His Word's relevant to the thread he started.
According to the bible, the "Covenants" that were changed pertain to the remission and justification of sins. Not the definition of sins. Before Christ there were Levitical Priesthood ceremonial, sacrificial "Works of the Law" for remission and justification of sins. Before Christ, if I sinned, I had to find a Levite Priest to perform ceremonial, sacrificial "Works or Deeds of the Law" contained in the Levitical Priesthood. Gentiles were not allowed to partake in these ceremonies. See Heb. 7-10. These fleshy, carnal "Works of the Law" were "ADDED" until the SEED should come. Gal. 3:19
Since the Mainstream Church of that time rejected Jesus as their Messiah, they continued to perform and preach these "Deeds of the Law" for justification of sin and rejected the idea that Grace, through faith is what cleansed and justified sins, not the designed "works of the Law" contained in the Law of Moses. As Paul told the Galatians:
Gal. 3:
1 O foolish Galatians,
who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you?
2 This only would I learn of you,
Received ye the Spirit by the works of the law, (Sprinkling goats blood on the alter as prescribed by the Levitical Priesthood)or by the hearing of faith? (Belief that it is Christ's blood that frees us from the death our transgression caused us).
So when Paul said "By works of the law shall no flesh by justified", he is speaking to the laws that were specifically designed for justification of sin, not the entire definition of God's Righteousness defined in the Old Testament.
This "Change in the law", (New Covenant) as Heb. 7 speaks to, has nothing to do with the definition of sin, only the remission of sin.
There is a widespread teaching, accepted by "Many", that preaches the New covenant replaces the entire "Mosiac" (as they call it) law structure which is there to define sin. (for by the Law is the knowledge of sin) This teaching is false as scriptures show us.
This explains why the Apostles in Acts 15 directed the New Converts to obey several of God's Commandments, then sending them to learn from Moses as Jesus instructed them to do in Mat. 23. And it explains why they didn't send them to the Sect of Pharisees which believed who preached they needed to be circumcised and "Command them to follow the Law of Moses, including animal sacrifice.
I hope that helps