That's false dispensational theory of Christendom. It's only Israel and nothing but Israel in both OT and NT.
You are dividing the scriptures as partly for Christendom and partly for future Israel. Whole scriptures are one unit:
2 Tim 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
That's the reason Christendom is divided over theology and doctrines. I walked out of Christianity several years back because it fails to understand the true gospel of the Hebrew Messiah.
In OT strangers could join Israel under one Torah - the same goes with NT because it's primarily written to Jews and lost sheep of the house of Israel wrongly tagged as gentiles. We can only be accepted if we are grafted among them:
Rom 11:17 And if some of the branches were broken off, and you, being a wild olive tree, have been grafted in among them, and came to share the root and fatness of the olive tree,
They are not grafted to Christianity but rather we are grafted among them.
We are grafted into God, not an O.T. belief system.
We are Grafted into God Himself, not Israel......
16 For if the firstfruit be holy, the lump(God) is also holy: and if the root(God) be holy, so are the branches.(Israel)
17 And if some of the branches(Israel) be broken off, and thou, being a wild olive tree, wert grafted in among them, and with thempartakest of the root and fatness of the olive tree(God)
18 Boast not against the branches.(Israel) But if thou boast, thou bearest not the root,(God) but the root(God) thee.
19 Thou wilt say then, The branches(Israel) were broken off, that I might be grafted in.(To God)
20 Well; because of unbelief they were broken off(from God), and thou standest by faith. Be not highminded, but fear:
21 For if God spared not the natural branches,(Israel) take heed lest he also spare not thee.
22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.(from God)
23 And they also, if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again.(to God)
There are 2 trees here.....God is the good olive tree and
all mankind is the wild olive tree(both Jew and Gentile)...
24 For if thou wert cut out of the olive tree which is wild by nature, and wert grafted contrary to nature into a good olive tree(God) how much more shall these, which be the natural branches(Israel), be grafted into their own olive tree?(God)
You see , God Himself is the good olive tree, sinful man, both Jew and Gentile is the branch grafted from a wild olive tree. Israel was not a tree, but grafted into a tree. Israel was a branch that PRECEDED the Gentiles, originally cut out of the wild olive tree, but GRAFTED into the good olive tree(God) many centuries before Pentecost......some say we are grafted into Israel, but we are really grafted into God Himself, not Israel. They too are also just branches, like us....
John
15 I am the true vine, and my Father is the husbandman.
2
Every branch(Jew or Gentile) in me that beareth not fruit he taketh away: and
every branch(Jew or Gentile) that beareth fruit, he purgeth it, that it may bring forth more fruit.
3 Now ye are clean through the word which I have spoken unto you.
4 Abide in me, and I in you. As the branch(Jew or Gentile) cannot bear fruit of itself, except it abide in the vine(God) no more can ye, except ye abide in me(God).
5 I am the vine,
ye are the branches(both Jew or Gentile) He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing.
6 If a man abide not in me, he is cast forth as a branch(Jew or Gentile), and is withered; and men gather them, and cast them into the fire, and they are burned.