Romans 9:7
nor
are they all children because they are the seed of Abraham; but, “In Isaac your seed shall be
called.”
The deniers of salvation by God's grace alone refuse to believe the calling is according to the promise of God made to Abraham that Abraham would be the father of a great nation of believers, that is those who are 'the called', 'to be saints', are the sons of Abraham and it is to the 'descendents of Abraham' alone that the promise of eternal life is given. It is those God has called whom Christ aids to salvation.
Hebrews 2
10 For it was fitting for Him, for whom
are all things and by whom
are all things, in bringing many sons to glory, to make the captain of their salvation perfect through sufferings. 11 For both He who sanctifies and those who are being sanctified
are all of one, for which reason He is not ashamed to call them brethren, 12 saying:
“I will declare Your name to My brethren;
In the midst of the assembly I will sing praise to You.”
13 And again:
“I will put My trust in Him.”
And again:
“Here am I and the children whom God has given Me.”
14 Inasmuch then as
the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage.
16 For indeed He does not give aid to angels, but He does give aid to the seed of Abraham. 17 Therefore, in all things He had to be made like
His brethren, that He might be a merciful and faithful High Priest in things
pertaining to God, to make propitiation for the sins of the people. 18 For in that He Himself has suffered, being tempted, He is able to aid those who are tempted.
The children mentioned here are not all people, but only the children whom God gave to Christ.
Those children are the descendents of Abraham, both jew and gentile.
The others who do not receive mercy to be saved from the Heavenly Father are the children of the devil planted in God's field.
Review the parable of the wheat and the tares. Indeed why would they be saved since they are not God's children whatsoever.
To be a child of God, you must be one of children of promise, now believers are as Isaac, children of promise whom God gave to Abraham as a gift. Salvation was not extended to
Ishmail since Ishmael was not a child of promise. God clearly states that through ISAAC your SEED SHALL BE THE CALLED>
Romans 9 most definitely teaches the both jew and gentile must be one of the called of God in order to obtain salvation, otherwise they are Satan's children who desire to do Satan's will. And wheat doesn't turn into tares, nor tares into the wheat, each tree bears its fruit according to its nature.
Romans 9
6 But it is not that the word of God has taken no effect. For they are not all Israel who are of Israel, 7 nor are they all children because they are the seed of Abraham; but, “In Isaac your seed shall be called.”8 That is, those who are the children of the flesh, these are not the children of God; but the children of the promise are counted as the seed. 9 For this is the word of promise: “At this time I will come and Sarah shall have a son.”
10 And not only this, but when Rebecca also had conceived by one man, even by our father Isaac 11 (for the children not yet being born, nor having done any good or evil, that the purpose of God according to election might stand, not of works but of Him who calls), 12 it was said to her, “The older shall serve the younger.” 13 As it is written, “Jacob I have loved, but Esau I have hated.”