Galatians chapter 3 verse 29 is commonly used among Christian churches to promote the idea of God dealing with a new Spiritual Israel, a term not found in the scripture, to replace a disobedient physical Israel. This however makes God a promise breaker since he was quite direct when he promised Abraham what would become of his seed.
"And if you are Christ's, then you are Abraham's seed, and heirs according to the promise."
Here is the contrapositive or equivalent statement.
If you are not Abraham's seed, or not heirs according to the promise then you are not Christ's.
Sounds a bit different doesn't it? Both statements are logically equivalent. What most people ignore or forget to deal with is the phrase "according to the promise". What promise? To whom was it made and about whom was it made? Who are the heirs. Can one arbitrarily change who the heir is after the death of the will maker, in this case the Christ?
The promise refers back to Abraham and the promises made to him concerning his heirs.
"When Abram was ninety-nine years old, Yahweh appeared to Abram and said to him, "I am Almighty God; walk before Me and be blameless.
2 And I will make My covenant between Me and you, and will multiply you exceedingly."
3 Then Abram fell on his face, and God talked with him, saying:
4 "As for Me, behold, My covenant is with you, and you shall be a father of many nations.
5 No longer shall your name be called Abram, but your name shall be Abraham; for I have made you a father of many nations.
6 I will make you exceedingly fruitful; and I will make nations of you, and kings shall come from you.
7 And I will establish My covenant between Me and you and your descendants after you in their generations, for an everlasting covenant, to be God to you and your descendants after you."
A good way to figure the above passage out is to ask yourself questions as you read it. You could start on verse 4 and ask who or what group of people of Abraham's descendants has he made into many nations with kings, who claim the God of Abraham as their God?
You can do this with many of the promises found in the Bible.
The God of Abraham, Isaac and Jacob keeps his promises. Our God does not lie. The clues in the Bible and archeology prove with out question that the Anglo-Saxon, Germanic, Scandinavian, Celtic and kindred peoples are true physical Israel.
The Archeological record fully supports who is physical Israel.
"The LORD" has been replaced with the original text YHVH or Yahweh, our God's name. All quotes from the NKJV.
Feel free to send your helpful comments.