Since Christendom consists primarily of Gentiles, this is incorrect. Christendom includes all the denominations and groups on earth who claim to be Christians. But the sad reality is that only a small fraction may be genuine. .....
The Jews as a subset of Jacob/Israel, excludes the 10 lost Ephramite tribes of the Israel Assyrian captivity, who has returned from their exile from all the nations of the four corners of the earth into Christendom, established by the Jews: the Jews Jesus / Yeshua, his jewish twelve disciples turned apostles, and the jewish early Christian convert, the apostle Paul.
As stated in Romans 11, describing the full olive tree, Body of Christ, most Jews were hardened until the completion of the time of the Gentiles, by the stumbling block, Jesus Christ / Yeshua ha'Maschiach. That however will change when the original cut off branches (Jews) will be grafted in together after the wild olive branches (Gentiles) have been grafted in (when the time of the Gentiles have come to fruition). The grafting in of the original cut-off branches (jews) of the olive tree, is starting to become reality, as we see with Messianic Judaism (like oneforisrael.com ). Ezekiel 37 - 48 prophesies of this earth's restored Israel / Christendom, and a coming temple, in which the Anti-Christ, Anti-Messiah will proclaim himself to be the only god to be worship in the last 3.5 years on this earth before the return of Jesus Christ / Yeshua ha'Maschiach. This all happens BEFORE THE RETURN OF CHRIST, AS THIS EARTH IS DESTROYED AT THE RETURN OF CHRIST, AND A NEW HEAVEN AND EARTH IS ESTABLISHED.
When God lift his spirit of stupor, and starts pouring out his spirit of grace, those of the Jews who are to be grafted into restored Israel / Christendom / the Body of Christ, they will mourn for the One we have pierced, for those of them who come to that realisation in time, before the return of the One we have pierced.
Zechariah 12 (ESV)
10 "And
I will pour out on the house of David and the inhabitants of Jerusalem
a spirit of grace and pleas for mercy, so that, when they
look on me, on him whom they have pierced, they shall mourn for him, as one mourns for an only child, and weep bitterly over him, as one weeps over a firstborn.
Romans 11 (ESV)
5 So too at the present time there is a remnant, chosen by grace.
7 What then? Israel failed to obtain what it was seeking. The elect obtained it, but the rest were hardened,
8 as it is written, "God gave them
a spirit of stupor, eyes that would not see and ears that would not hear, down to this very day."
11 So I ask, did they stumble in order that they might fall? By no means! Rather
through their trespass salvation has come to the Gentiles (Ephraimite part of Israel were scattered into, and adopted and intermingled with Gentiles), so as to make Israel (
the Jewish part of Israel) jealous.
12 Now if their trespass means riches for the world, and if their failure means riches for the Gentiles, how much more will their full inclusion mean!
13 Now I am speaking to you Gentiles. Inasmuch then as I am an apostle to the Gentiles, I magnify my ministry
14 in order somehow to make my fellow Jews jealous, and thus save some of them.
15 For if their rejection means the reconciliation of the world, what will their acceptance mean but life from the dead?
16 If the dough offered as firstfruits is holy, so is the whole lump, and if the root is holy, so are the branches.
17 But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree,
18 do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you.
19 Then you will say, "Branches were broken off so that I might be grafted in."
20 That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but fear.
21 For if God did not spare the natural branches, neither will he spare you.
22 Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness. Otherwise you too will be cut off.
23 And even they, if they do not continue in their unbelief, will be grafted in, for God has the power to graft them in again.
24 For if you were cut from what is by nature a wild olive tree, and grafted, contrary to nature, into a cultivated olive tree, how much more will these, the natural branches, be grafted back into their own olive tree.
25 Lest you be wise in your own sight, I do not want you to be unaware of this mystery, brothers: a partial hardening has come upon Israel, until the fullness of the Gentiles has come in.
26 And in this way all Israel will be saved, as it is written, "The Deliverer will come from Zion, he will banish ungodliness from Jacob";
27 "and this will be my covenant with them when I take away their sins."
28 As regards the gospel, they are enemies for your sake. But as regards election, they are beloved for the sake of their forefathers.
29 For the gifts and the calling of God are irrevocable.
30 For just as you were at one time disobedient to God but now have received mercy because of their disobedience,
31 so they too have now been disobedient in order that by the mercy shown to you they also may now receive mercy.
32 For God has consigned all to disobedience, that he may have mercy on all.
33 Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!
34 "For who has known the mind of the Lord, or who has been his counselor?"
35 "Or who has given a gift to him that he might be repaid?"
36 For from him and through him and to him are all things. To him be glory forever. Amen.