The True Israel, the Church are those people who have Abraham’s spiritual faith regardless of their ethnicity Gal 3:7,26-29
7 Know ye therefore that they which are of faith, the same are the children of Abraham[Israel].
26 For ye are all the children of God by faith in Christ Jesus.
27 For as many of you as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.122
29 And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.
Rom 4:16
16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
Gal 6:16
16 And as many as walk according to this rule[rule of faith], peace be on them, and mercy, and upon the Israel of God.
When you look deeply into Galatians 3 (and I have), what you will find is that the covenant of righteousness by faith in the gospel of Jesus Christ came to Abraham in Genesis 15-17. Therefore, the covenant of righteousness (salvation) by faith in the gospel actually pre-dates the Law of Moses by 430 years.
Gal 3:14-17 NASB 14 in order that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we would receive the promise of the Spirit through faith. 15 Brethren, I speak in terms of human relations: even though it is [only] a man's covenant, yet when it has been ratified, no one sets it aside or adds conditions to it. 16 Now the promises were spoken to Abraham and to his seed. He does not say, "And to seeds," as [referring] to many, but [rather] to one, "And to your seed," that is, Christ. 17 What I am saying is this: the Law, which came four hundred and thirty years later, does not invalidate a covenant previously ratified by God, so as to nullify the promise.
So the question of this thread demonstrates a theological error since the covenant of Faith predates the covenant of The Law. "Has the church replaced Israel?" is the wrong question. The right question would be "Did the Jews replace the Abrahamic covenant given to the Father of Many Nations with a single-nation-only theology?" For Paul says Abraham was a gentile when God made him righteous for his faith in the gospel:
Rom 4:3, 9-13, 16-17 NASB 3 For what does the Scripture say? "ABRAHAM BELIEVED GOD, AND IT WAS CREDITED TO HIM AS RIGHTEOUSNESS." ... 9 Is this blessing then on the circumcised, or on the uncircumcised also? For we say, "FAITH WAS CREDITED TO ABRAHAM AS RIGHTEOUSNESS." 10 How then was it credited? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised; 11 and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them, 12 and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. 13 For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith. ... 16 For this reason [it is] by faith, in order that [it may be] in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, 17 (as it is written, "A FATHER OF MANY NATIONS HAVE I MADE YOU") in the presence of Him whom he believed, [even] God, who gives life to the dead and calls into being that which does not exist.
Isa 54:1 NASB 1 "Shout for joy, O barren one, you who have borne no [child;] Break forth into joyful shouting and cry aloud, you who have not travailed; For the sons of the desolate one [will be] more numerous Than the sons of the married woman," says the LORD.
The sons of the desolate one who didn't physically give birth are Christians. The sons of the married woman who is Sarah who gave birth to the physical Jews. This passage in ISA 54 is quoted by Paul in Gal 4 when he describes the two women as two covenants - The Law and Faith.
Often we see prophecy where both Jacob and Israel are mentioned. This shows that God is speaking to both physical Jews and Christians.
1Ch 16:13-18 NASB 13 O seed of Israel His servant, Sons of Jacob, His chosen ones! 14 He is the LORD our God; His judgments are in all the earth. 15 Remember His covenant forever, The word which He commanded to a thousand generations, 16 [The covenant] which He made with Abraham, And His oath to Isaac. 17 He also confirmed it to Jacob for a statute, To Israel as an everlasting covenant, 18 Saying, "To you I will give the land of Canaan, As the portion of your inheritance."
So if we ponder these things deeply we should arrive at the conclusion that God always intended a dual simultaneous meaning of both Jews and Christians to be counted as covenant peoples. This is represented in Israel itself by the upper 10 tribes and lower 2 tribes (lower 2 included JEWdah) being separate "kingdoms." But consider... God had already created the covenant of faith with Abraham ... then 430 years later continued on to make covenants with Moses, the nation of Israel, David, and others and treat them and call that nation his chosen people. Clearly neither Jews nor Christians have "replaced" one another in God's eyes.
Deu 7:6-9 NASB 6 "For you are a holy people to the LORD your God; the LORD your God has chosen you to be a people for His own possession out of all the peoples who are on the face of the earth. 7 "The LORD did not set His love on you nor choose you because you were more in number than any of the peoples, for you were the fewest of all peoples, 8 but because the LORD loved you and kept the oath which He swore to your forefathers, the LORD brought you out by a mighty hand and redeemed you from the house of slavery, from the hand of Pharaoh king of Egypt. 9 "Know therefore that the LORD your God, He is God, the faithful God, who keeps His covenant and His lovingkindness to a thousandth generation with those who love Him and keep His commandments;