Certainly, but "they are not all Israel, which are of Israel."
Your misunderstanding obscures the Good News of the Gospel and denies the genuine sorrow Paul felt for those Jews who did not believe in Jesus Christ...
That I have great heaviness and continual sorrow in my heart. For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises; Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen. Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. For this is the word of promise, At this time will I come, and Sarah shall have a son. And not only this; but when Rebecca also had conceived by one, even by our father Isaac; (For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth;) It was said unto her, The elder shall serve the younger." -- Romans 9:1-12"I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost,
Certainly, but "they are not all Israel, which are of Israel."
"Do not say 'We have Abraham for our father' for I tell you that God could raise up from these stones descendants to Abraham"
"If you are in Christ, you are Abraham's descendants and heirs according to the promise."
What then? Israel failed to obtain what it was seeking. The elect obtained it, but the rest were hardened, 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."
And David says,
"Let their table become a snare and a trap,
a stumbling block and a retribution for them;
let their eyes be darkened so that they cannot see,
and bend their backs forever."
Now I am speaking to you Gentiles. Inasmuch then as I am an apostle to the Gentiles, I magnify my ministry in order somehow to make my fellow Jews jealous, and thus save some of them. For if their rejection means the reconciliation of the world, what will their acceptance mean but life from the dead? If the dough offered as firstfruits is holy, so is the whole lump, and if the root is holy, so are the branches.
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, 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. Then you will say, "Branches were broken off so that I might be grafted in." That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe. For if God did not spare the natural branches, neither will he spare you. 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. 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. 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.