Exodus 31:13
“Say to the Israelites, ‘You must observe my Sabbaths.
This will be a sign between me and you for the generations to come,
so you may know that I am the Lord, who makes you holy.
Ezekiel 20:12
Also I gave them my Sabbaths as a sign between us,
so they would know that I the Lord made them holy.
Ezekiel 20:20
Keep my Sabbaths holy, that they may be a sign between us.
Then you will know that I am the Lord your God.”
God's ISREAL are all those who BELIEVE and FOLLOW God's WORD. If you are not a part of God's ISRAEL you have no part in the NEW COVENANT. *Hebrews 8:10-12
Gentiles are now grafted in to God's ISRAEL (Romans 11:16:27)
HEBREWS 8:10-12
[10]
For this is the covenant that I will make with the HOUSE OF ISREAL after those days, said the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
[11], And they shall not teach every man his neighbor, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest.
[12], For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
[13], In that he said, A new covenant, he has made the first old. Now that which decays and waxes old is ready to vanish away.
ROMANS 11:16-27
[16], For if the first fruit be holy, the lump is also holy: and if the root be holy, so are the branches.
[17], And if some of the branches be broken off, and
you, being a wild olive tree, were grafted in among them, and with them partake of the root and fatness of the olive tree;
[18], Boast not against the branches. But if you boast, you bore not the root, but the root you.
[19], You will say then, The branches were broken off,
that I might be grafted in.
[20], Well; because of unbelief they were broken off, and you stand by faith. Be not high minded, but fear:
[21], For if God spared not the natural branches, take heed lest he also spare not you.
[22], Behold therefore the goodness and severity of God: on them which fell, severity; but toward you, goodness, if you continue in his goodness: otherwise you also shall be cut off.
[23], And they also, if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again.
[24], For if you were cut out of the olive tree which is wild by nature,
and were grafted contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be grafted into their own olive tree?
[25], For I would not, brothers, that you should be ignorant of this mystery, lest you should be wise in your own conceits; that blindness in part is happened to Israel, until the fullness of the Gentiles be come in.
[26], And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:
[27], For this is my covenant to them, when I shall take away their sins.
Hope this helps