"If dispensationalism accepts Romans 11: 1-5 as being a remnant of Old Covenant Israel who were born again in Christ and became new creatures or creations, then dispensationalism would claim that there can be no Gentile remnant, using its extreme division between saved Gentile and saved Jew, which the quote above from Ephesians 2: 11-17 shows does not agree with New Testament scripture, Believing Gentiles become part of Israel, but this is not Old Covenant Israel of the flesh, and Paul is calling it the Israel of God in Galatians 6: 15-16."
"From the time of Christ’s rejection by Israel until the time when God deals specifically with Israel again in the seventieth week it is not possible to refer to a remnant of the nation Israel." Things to Come: A Study in Biblical Eschatology, 1965, by J. Dwight Pentecost
Pentecost is apparently following the dispensationalist extreme division between Old Covenant Israel and the Church. Though he is talking about the period of the Church Age here, he appears to be focusing only on a remnant of those of physical Israel, separating out all who are of the physical bloodline from the Gentile believers.
Romans 10: 12 and Galatians 3: 28, as well as Ephesians 2: 11-15 teach that there is a unity between Jews and Gentiles who are born again by the Spirit from the Gospel of Christ and become new creatures or creations.
In making its extreme division between Old Covenant Israel and the Church and ignoring the three New Testament scriptures in the sentence above, the founders of dispensationalism created a set of false doctrines which disagree with New Testament scripture.
"Believing Gentiles become part of Israel,(Ephesians 2: 13) but this is not Old Covenant Israel of the flesh, and Paul is calling it the Israel of God in Galatians 6: 15-16."
"For in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creature.
16.And as many as walk according to this rule, peace be on them, and mercy, and upon the Israel of God." Galatians 6: 15-16
Those who are made into new creatures or new creations by believing the Gospel of Christ are born again (John 3: 1-6), and become part of the elect of God, which is a unity, not divided into Gentiles and Jews, though it can and is called the Body of Christ or in Galatians 6: 16 the Israel of God.
"15.For in Christ Jesus. The reason why he is crucified to the world, and the world to him, is, that in Christ, to whom he is spiritually united, nothing but a new creature is of any avail. Everything else must be dismissed, must perish. I refer to those things which hinder the renewing of the Spirit. “If any man be in Christ” says he, “let him be a new creature.” (2 Corinthians 5:17.) That is, if any man wishes to be considered as belonging to the kingdom of Christ, let him be created anew by the Spirit of God; let him not live any longer to himself or to the world, but let him be raised up to “newness of life.” (Romans 6:4.) His reasons for concluding that neither circumcision nor uncircumcision is of any importance, have been already considered. The truth of the gospel swallows up, and brings to nought, all the shadows of the law."
"And upon the Israel of God (101) This is an indirect ridicule of the vain boasting of the false apostles, who vaunted of being the descendants of Abraham according to the flesh. There are two classes who bear this name, a pretended Israel, which appears to be so in the sight of men, — and the Israel of God. Circumcision was a disguise before men, but regeneration is a truth before God. In a word, he gives the appellation of the Israel of God to those whom he formerly denominated the children of Abraham by faith, (Galatians 3:29,) and thus includes all believers, whether Jews or Gentiles, who were united into one church. On the contrary, the name and lineage are the sole boast of Israel according to the flesh; and this led the apostle to argue in the Epistle to the Romans, that “they are not all Israel which are of Israel, neither because they are the seed of Abraham, are they all children.” (Romans 9:6.)"
This is John Calvin's commentary on Galatians 6: 15-16 - the link is
https://www.studylight.org/commentaries/cal/galatians-6.html
And the interpretation of Galatians 6: 15-16 above is part of Reformation Theology.
Dispensationalism is somewhat similar to Transformational Marxism and its Identity Politics or Political Correctness. Transformational Marxism operates on divisions by race, gender, sexual orientation etc and identifies those on the wrong side of divisions as enemies. Dispensationalism operates on the basis of divisions, such as Old Covenant Israel and the Church, or the division between even saved Jews and saved Gentiles and on and on. Dispensationalism is based upon division though it does not always identify as enemies those on one particular side of a division. In the case of "replacement theology" it is the enemy for dispensationalism, when it, as far as New Testament scripture is concerned, is divided from dispensationalism.
This means that what dispensationalists call "replacement theology" which seems to be Reformation Theology, though not always certain, is the enemy.
Dispensationalism then becomes the "ἀντιθέσεις," or antitheoeis, or anti-thesis, in I Timothy 6: 20 to not only Reformation Theololgy but to several New Testament texts, some listed above.
