Opinions are like noses...
Ohhhh, yes they are.... This should be clearly seen in Hebrews 1:1-2, that "Long ago, at many times and in many ways,
God spoke to our fathers by the prophets, but
in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world." We are all one, the Israel of God. Those of us who are actually in Christ, that is...
And are part of the Israel of God. It should be clearly seen in what Paul says in Romans 11, that "a partial hardening has come upon Israel, until the fullness of the Gentiles has come in, and in this way
all Israel will be saved." The Israel of God consists of all those who are in Christ at any given point in time, past, present, and future.
Well, with regard to "Christians" you mean to say all of those who
claim to be Christians, and in that case I agree that yes, there are some (many) folks in this world who
claim to be Christians but are not. Not that I or anyone else can positively tell who they are at present, but for sure, many will (in the words of John) go out from us, proving, or making it plain, that they are not of us (1 John 2:19).
No one was ever physically born into Israel, either. I'm going to address each separately:
"You cannot apply Israel onto the church."
John (and Jesus, as quoted by John), Paul, and Peter do exactly that. I wish the folks who see such a disconnection from the Old Testament to the New ~ as if they are two different stories. The Bible is one story of one people of God from Genesis to Revelation.
"No one is physically born into the church."
I do agree that no one is physically born into Christ's church. But likewise, again, no child was ever, even in Old Testament times, born into the Israel of God, even when born of Israelite parents. It's quite the same thing, either way we go in time; not all who are descended from Israel belong to Israel. Children are certainly welcomed into the community of Israel officially when they were circumcised at eight days old according to the command of God in the Old Testament and baptized since the days of John the Baptist and especially Peter's sermon in Acts 2 ("Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. For the promise is for you and for your children and for all who are far off...") as early as possible (Christian parents should have their babies baptized).
So yes, here you're affirming what I thought you may have meant above. Yes, I agree. And not part of the Israel of God. Agreed!
Right, well, the branches you're talking about are those who were physically descended from Abraham, Isaac, and Jacob. Sure. And the beat goes on...
Yeah, there's... nothing new under the sun. :) Yes, if one is truly born again of the Holy Spirit, then, well, nobody says it better than Peter:
"Blessed be the God and Father of our Lord Jesus Christ! According to His great mercy, He has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you, who by God’s power are being guarded through faith for a salvation ready to be revealed in the last time" (1 Peter 1:3-5).
Yes, physical lineage does not in any way determine who is elect of God, of God's Israel, in Christ. I've said that many times.
Grace and peace to you.