Replacement Theology is False Teaching

I don't want you to be ignorant of this mystery, brothers and sisters, so that you will not be conceited: A partial hardening has come upon Israel until the fullness of the Gentiles has come in. (Romans 11:25 CSB)

Gentile Christians do not replace Israel. Rather, they are grafted into Israel. Replacement Theology is a false teaching by conceited Christians.

"In that day I will restore the fallen house of David. I will repair its damaged walls. From the ruins I will rebuild it and restore its former glory. And Israel will possess what is left of Edom and all the nations I have called to be mine." The Lord has spoken, and he will do these things. (Amos 9:11-12 NLT)

"Shout for joy and be glad, O Daughter of Zion, for I am coming to dwell among you," declares the LORD. "On that day many nations will join themselves to the LORD, and they will become My people. I will dwell among you, and you will know that the LORD of Hosts has sent Me to you. And the LORD will take possession of Judah as His portion in the Holy Land, and He will once again choose Jerusalem. Be silent before the LORD, all people, for He has roused Himself from His holy dwelling." ((Zechariah 2:10-13 BSB)

I am saying all this especially for you Gentiles. God has appointed me as the apostle to the Gentiles. I stress this, for I want somehow to make the people of Israel jealous of what you Gentiles have, so I might save some of them. For since their rejection meant that God offered salvation to the rest of the world, their acceptance will be even more wonderful. It will be life for those who were dead! And since Abraham and the other patriarchs were holy, their descendants will also be holy - just as the entire batch of dough is holy because the portion given as an offering is holy. For if the roots of the tree are holy, the branches will be, too. But some of these branches from Abraham's tree - some of the people of Israel - have been broken off. And you Gentiles, who were branches from a wild olive tree, have been grafted in. So now you also receive the blessing God has promised Abraham and his children, sharing in the rich nourishment from the root of God's special olive tree. But you must not brag about being grafted in to replace the branches that were broken off. You are just a branch, not the root. "Well," you may say, "those branches were broken off to make room for me." Yes, but remember - those branches were broken off because they didn't believe in Christ, and you are there because you do believe. So don't think highly of yourself, but fear what could happen. For if God did not spare the original branches, he won't spare you either. Notice how God is both kind and severe. He is severe toward those who disobeyed, but kind to you if you continue to trust in his kindness. But if you stop trusting, you also will be cut off. And if the people of Israel turn from their unbelief, they will be grafted in again, for God has the power to graft them back into the tree. You, by nature, were a branch cut from a wild olive tree. So if God was willing to do something contrary to nature by grafting you into his cultivated tree, he will be far more eager to graft the original branches back into the tree where they belong. (Romans 11:13-24 NLT)