Romans 9 begins a section dealing specifically with the Jews and their current standing before God. Calvinists mistake this chapter for a complete change of topic so Paul can give them proof texts for their gnostic philosophy, but that is not the case.
In Romans 9:6 the Holy Spirit says through Paul that "...they are not all Israel, which are of Israel" and then in verse 8 the thought is concluded: "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."
The Jews considered themselves to be the chosen people of God and highly favored by Him. Consequently, verses like the ones mentioned above would have been quite startling for Jewish readers who took immense pride in their heritage and history. They also had such a hatred for Gentiles that they wouldn't even eat with them, and it was an appalling thought for them to consider that Gentiles could be in the family of God. They were extremely possessive about "their God" and so Paul makes it clear that it is God who sets the terms of salvation, and who His people are, and God is fully just in doing so.
Since the children of the flesh (Jews) have been rejected as the people of God as stated above, does that mean God is unjust? Romans 9:14 asks this question: What shall we say then? Is there unrighteousness with God? God forbid.
Paul’s purpose for the chapters 9-11 is to answer this question with a conclusive 'No.'
So Paul explains further the reasoning that God is fully able to choose who He will have mercy on and who He will harden by giving an example of Pharaoh (someone who rejected God, hardened his own heart, and who was temporarily given a hardened heart by God for specific purposes).
In Romans 9:21-22 we read, Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour? 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:
Who are the vessels unto honor and dishonor? Verse 22 explains by saying "vessels of wrath fitted for destruction" which God endured with much long suffering. They were not made vessels of wrath by God, but by themselves after they had filled up the measure of their sins, and thereby fitted themselves as vessels for destruction. God endured the Jews with much long-suffering, though they received their judgment to the uttermost at last (cf. 1 Thessalonians 2:15-16; Matthew 21:43; Luke 13:34).
So the vessels of dishonor or wrath are Jews according to the flesh, and the vessels of mercy or honor are those who enter the Kingdom by faith, the spiritual seed of Abraham, which is an offer extended to all people both Jew and Gentile although the vast majority of Jews have always rejected the gospel.
Next, Paul quotes from Hosea 2:23 and then Hosea 1:10 to prove from the Old Testament that it was prophesied that the nation of Israel would be rejected and replaced.
Romans 9:25-26, As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved. And it shall come to pass, that in the place where it was said unto them, Ye are not my people; there shall they be called the children of the living God.
We'll now look through Hosea 1 at the verses pertaining to this topic.
Hosea 1:6, And she conceived again, and bare a daughter. And God said unto him, Call her name Loruhamah: for I will no more have mercy upon the house of Israel; but I will utterly take them away.
The 10 tribes of the northern kingdom of Israel has been taken away as promised.
Hosea 1:7, But I will have mercy upon the house of Judah, and will save them by the Lord their God, and will not save them by bow, nor by sword, nor by battle, by horses, nor by horsemen.
This purpose of this physical deliverance was to protect Judah so that the promised Messiah would come as prophesied. This verse foretells of Judah being saved from Sennacherib and the Assyrians in the days of Hezekiah, when in one night the angel of the Lord smote a hundred and eighty-five thousand of the flower of the Assyrian host.
Hosea 1:8-9, Now when she had weaned Loruhamah, she conceived, and bare a son. Then said God, Call his name Loammi: for ye are not my people, and I will not be your God.
The ultimate rejection of the Jews (the collective house of Israel and Judah) as a people is here prophesied. They will not be the people of God and He will no longer be their God.
After Judah's return from Babylon, the distinction between Israel and Judah was largely destroyed, and those of them that did return were all included under one label: Jews, which are the vessels of wrath.
Hosea 1:10, Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye are not my people, there it shall be said unto them, Ye are the sons of the living God.
This verse quoted by Paul in Romans 9:26 is an extension of the promise of Genesis 32:12 that those the faith, the children of Abraham (Galatians 3:29), will be numerous. In the place of the reprobated people there shall be found an Israel of many people that shall be the children of the living God. This is the spiritual Israel, the Israel of God. To those that were not the people of God (Gentiles), they will become the people of God by faith as the true Israel which has now happened.
1 Peter 2:10, Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.
Hosea 1:11, Then shall the children of Judah and the children of Israel be gathered together, and appoint themselves one head, and they shall come up out of the land: for great shall be the day of Jezreel.
The primary intention of the prophesy is that the Lord Jesus Christ shall become the chief and the king of one family, composed of Judah and Israel, of Jews and Gentiles.
Now looking to Hosea 2:23, the verse Paul quotes first in Romans 9:25, we read, And I will sow her unto me in the earth; and I will have mercy upon her that had not obtained mercy; and I will say to them which were not my people, Thou art my people; and they shall say, Thou art my God.
As a nation, Israel has been rejected, and the Gentiles have been brought in by faith.
As Paul concludes in Romans 10:11-13, For the scripture saith, Whosoever believeth on him shall not be ashamed. For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him. For whosoever shall call upon the name of the Lord shall be saved.
There is only ONE people of God, regardless of heritage, and that is believers in Christ. Ephesians 2 elaborates on this still further.
1 Thessalonians 2:15-16, Who both killed the Lord Jesus, and their own prophets, and have persecuted us; and they please not God, and are contrary to all men: Forbidding us to speak to the Gentiles that they might be saved, to fill up their sins alway: for the wrath is come upon them to the uttermost.
