The Sabbath keeping of a jew is not a substitute for receiving Messiah. Rejecting Messiah while keeping Sabbaths is having missed the revelation of God.
14 But their minds were hardened; for until this very day at the reading of the old covenant the same veil remains unlifted, because it is removed in Christ. 15 But to this day whenever Moses is read, a veil lies over their heart; 16 but whenever a person turns to the Lord, the veil is taken away. 17 Now the Lord is the Spirit, and where the Spirit of the Lord is, there is liberty. 2 Cor
In Romans 11 Paul explains that All Israel will be saved, but it is not through having kept the Sabbath, it is though receiving Messiah.
What then? What Israel is seeking, it has not obtained, but those who were chosen obtained it, and the rest were hardened; 8 just as it is written,
“God gave them a spirit of stupor,
Eyes to see not and ears to hear not,
Down to this very day.”
Jews are enemies of the gospel, but beloved because of the calling of God and the forefathers, they are being reconciled to God via deliverance from the enmity- the law contained in commandments, and made one with all flesh in the perfect law of liberty under the headship of Chirst within the one new man.
But now in Christ Jesus you who formerly were far off have been brought near by the blood of Christ. 14 For He Himself is our peace, who made both groups into one and broke down the barrier of the dividing wall, 15 by abolishing in His flesh the enmity, which is the Law of commandments contained in ordinances, so that in Himself He might make the two into one new man, thus establishing peace, 16 and might reconcile them both in one body to God through the cross, by it having put to death the enmity. 17 And He came and preached peace to you who were far away, and peace to those who were near; 18 for through Him we both have our access in one Spirit to the Father.
The gospel is the Sabbath for all who hear, and Today is the Day that the Lord has made, if we have entered it, ceasing from our own works(no longer living for self but in service to Messiah).
Therefore, let us fear if, while a promise remains of entering His rest, any one of you may seem to have come short of it. 2For indeed we have had good news preached to us, just as they also; but the word they heard did not profit them, because it was not united by faith in those who heard…
He again fixes a certain day, “Today,” saying through David after so long a time just as has been said before,
“TODAY IF YOU HEAR HIS VOICE,
DO NOT HARDEN YOUR HEARTS.”
For if Joshua had given them rest, He would not have spoken of another day after that. 9So there remains a Sabbath rest for the people of God. 10For the one who has entered His rest has himself also rested from his works, as God did from His. 11Therefore let us be diligent to enter that rest, so that no one will fall, through following the same example of disobedience. 12For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart. 13And there is no creature hidden from His sight, but all things are open and laid bare to the eyes of Him with whom we have to do.
Verses 12,13 is quoted a lot, but rarely in context with the subject it is attached to by the writer of Hebrews- entering the Sabbath rest of the believer. (I have died, Christ lives through me, and the life I live in the flesh I live by the faith of the son of God.)