Israel was God chosen people but they were rejected, and died in the desert, so yes, the children of God can be rejected. Paul said we are grafted into the people of God because the jews got rejected.
We are warned not to fall into the same sin as Israel and therefore end up rejected also, but it appears you do not accept what Paul is saying. God bless you
Israel are the true servants of God and the Tribe failed due to the workings of Satan as were the Jews, but some of the Israelites were still true to God in fact, called the remain, we see this in they who followed Jesus Christ, as Jesus said to Nathaniel that he was a true Israelite and we see where Jesus said to his disciples go to the Israelites and if they reject you, to leave from such people directly and take nothing at all from them at all, not even the sand on their sandals. because such who claim to be Israelites are not truly worthy of being an Israelite at all in fact.
One is grafted in as regards to abiding in the Tree, just as anyone is. It's a Spiritual Tree ? Satan claims that the Jews are a race, but they were a Spiritual Tribe as it's foundation in God. One tribe of Semitic people out of many Semitic Tribes back in the days in fact.
Satan works create delusions among people, so we see nowadays that their is a great stupid taboos made up, like the concept of Anti-Semitic ? this is pathetic ! no Christian is debating about the Race of the so called Jews at all, not to mention that Islam is like 90% of the Semitic people nowadays. fact is that Christianity is not talking about a Race of people at all, in fact it says that under Christianity their is nether Jew or Gentile, anyone who claims otherwise is of Satan !
The Jews today are not worthy at all because they are totally lost as to Jesus Christ in fact, remember that No one comes to the Father but through his only begotten Son. So they who do not have the Holy Spirit are total lost as to God.
There are only about 10% of people in the world today who could even be regarded as worthy Jews in the world today, only because they abide in the OT, the rest claiming to be Jews are not even worthy of that.
It has nothing to do with ones Race at all ! and anyone who has the Holy Spirit knows that's a fact. no ones Race is going to Save you ! it does not work like that. the Jews back in the day were regarded as worthy of God and that's why they were chosen.
Idolising People is a great Sin, such is only worthy of Satan.