Dispensationalist falsely teach that God dealt with Israel before the cross, but since the cross He has been dealing with the Church, but after the rapture He will once again turn His attention toward Israel. This is also a false teaching. Their problem is not only do they have no scripture to corroborate this belief, but it directly opposes what the Bible does teach on the matter. Here are a few passages on what God does have to say about the union between Israel and the Church.
Romans 2:28-29
28 For he is not a Jew, which is one outwardly; neither is circumcision, which is outward in the flesh:
29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Romans 10:12 For there is no difference between Jew and the Greek: for the same Lord is rich unto all that call upon his name.
Romans 11:16-24
16 For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches.
17 And if some of the branches be broken off, and thou being a wild olive tree, wert grafted in among them, and with them partake of the root and fatness of the olive tree:
18 Boast not against the branches. But if thou boast thou bearest not the root, but the root thee.
19 Thou wilt say then, the branches were broken off that I might be grafted in.
20 Well: because of unbelief they were broken off, and thou standeth by faith. Be not high minded but fear.
21 For if God spared not the natural branches, take heed lest he also spare not thee.
22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee goodness, if thou continue in his goodness: otherwise thou shall also be cut off.
23 And they also if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again.
24 For if thou wert cut out of the olive tree that is wild by nature, and were grafted in contrary to nature into the good olive tree: how much more shall these, which be the natural branched be grated into there own olive tree?
Romans 12:5 So we being many, are one body in Christ, and every one member one of another.
Galatians 3:28-29
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female, for you are all one in Christ Jesus.
29 And if you be Christ's, then you are Abraham's seed, and heirs according to the promise.
Galatians 6:15-16
15 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 upon them, and mercy, and upon the Israel of God.
Ephesians 2:11-19
11 Wherefore remember, that ye being in times past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands.
12 That at times past you were without Christ, being aliens from the commonweath of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ.
14 For He is our peace, who hath made both one, and hath broken down the middle wall of partition between us;
15 Having abolished in His flesh the enmity, even the law of commandment in ordinances; for to make in Himself of twain one new man, so making peace;
16 And that He might reconcile both unto God in one body by the cross, having slain the enmity thereby:
17 And came and preached peace to you that were afar off, and to them that were nigh.
18 For through Him we both have access by one Spirit unto the Father.
19 Now therefore ye are no more strangers and foreigners, but fellow citizens with the saints, and of the household of God.
Ephesians 4:4-6
4 There is one body, and one Spirit, even as you are called in one hope of your calling;
5 One Lord, one faith, one baptism,
6 One God and Father of us all, who is above all, and through us all, and in you all.
We can clearly see that scripture teaches, the Jew and Gentile/Israel and the Church have become one new man. That there is only one Faith, and that we are all apart of the same body in Christ. That a Jew is not one that is a Jew outwardly, but a Jew is one that is one inwardly circumcised in the heart by the Spirit, regardless of blood line. Scripture tells us that believing Gentiles have been grafted into the good Olive Tree which is Israel, who's root is Christ, and whoever has been baptized into Christ, have become citizens of the true Israel of God with the saints, being seeds of Abraham, heirs according to the promise. We have not replaced Israel at all, but we are included with them in all the promises of God, being one with and equal to them, not separate from them in any way.