V.8 is comparing natural unbelieving Israel with natural believing Israel.
It has nothing to do with the false teaching that the Church is now Israel.
You (Falsely) suggest that Romans 9:6-8 below applies exclusively to (Jews) of the flesh?
The verses highlighted below in red clearly shows your claims to be (False), as it applies to those (Elected) to salvation, both Jew and Gentile, (The Church)
Romans 9:6-24KJV
6 Not as though the word of God hath taken none effect.
For they are not all Israel, which are of Israel:
7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
8 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.
9 For this is the word of promise, At this time will I come, and Sarah shall have a son.
10 And not only this; but when Rebecca also had conceived by one, even by our father Isaac;
11 (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
12 It was said unto her, The elder shall serve the younger.
13 As it is written, Jacob have I loved, but Esau have I hated.
14 What shall we say then? Is there unrighteousness with God? God forbid.
15 For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion.
16 So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy.
17 For the scripture saith unto Pharaoh, Even for this same purpose have I raised thee up, that I might shew my power in thee, and that my name might be declared throughout all the earth.
18 Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth.
19 Thou wilt say then unto me, Why doth he yet find fault? For who hath resisted his will?
20 Nay but, O man, who art thou that repliest against God? Shall the thing formed say to him that formed it, Why hast thou made me thus?
21 Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour?
22 What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23 And that he might make known the riches of his glory on
the vessels of mercy, which he had afore prepared unto glory,
24
Even us, whom he hath called, not of the Jews only, but also of the Gentiles?