Now where is the Body of Christ grafted into Israel?
ok, I'll do my best to show this.
First I want to point out where we see “the Israel of God” as opposed to “Israel after the flesh”, for any who haven’t noticed this, and how the Israel of God is made up of citizens who are “new creatures”, while Israel after the flesh is made up of unbelieving Jews/Israelites:
Gal 6:13-16
For neither they themselves who are circumcised keep the law; but desire to have you circumcised, that they may glory in your flesh.
But God forbid that I should glory, save in the cross of our Lord Jesus Christ, by whom the world is crucified unto me, and I unto the world.
For
in Christ Jesus neither circumcision availeth any thing, nor uncircumcision, but a new creature.
And as many as walk according to this rule, peace be on them, and mercy, and upon the Israel of God.
And this below makes mention of “Israel after the flesh”, which is earthly Israel whose citizens are not new creatures but they are unbelieving Jews under the Law:
1Co 10:18
Behold
Israel after the flesh: are not they which eat of the sacrifices partakers of the altar?
Here below we see unbelieving Gentiles are likewise called “Gentiles in the flesh”, the same as unbelieving Israel, and also we see that the Israel of God is allegorically called a commonwealth, which is a group of nations joined together under one ruler or government….like we have the example of a group of English speaking nations under the British monarchy and they are called a commonwealth. Believing Gentiles are joined together with believing Jews in the Israel of God, and become partakers of the same “root”, under the same ruler, Christ Jesus, King of Israel:
Eph 2:11-16
Wherefore remember, that ye being in time past
Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands;
That
at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
But now
in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ.
For he is our peace,
who hath made both one, and hath broken down the middle wall of partition between us;
Having abolished in his flesh the enmity, even the law of commandments contained in ordinances;
for to make in himself of twain one new man, so making peace;
And
that he might reconcile both unto God in one body by the cross, having slain the enmity thereby
The body of Christ is made up of both believing Jews and Gentiles who together are the "one new man" with both being part of the same tree partaking of the same root.
The analogy of the Israel of God being a commonwealth which members include believers of other nations agrees with the analogy of natural and unnatural branches being grafted together into the same tree (Israel of God, the kingdom of God) and all partaking of the same root (Israel’s Messiah and King Jesus Christ):
Rom 11:15-17
For if the casting away of them be the reconciling of the world, what shall the receiving of them be, but life from the dead?
For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches.
And if some of the branches be broken off, and
thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree