God tells us in this passage God has broken off the natural branches, Israel, from the root, and grafted in wild branches, the Gentiles, (Christians) into the root.  Many Israeli folks embraced Jesus Christ and become the early Christian Church.   But, nationally Israel refused the Messiah, and per Jesus' prophesy Jerusalem including the Temple was destroyed by the Roman forces in 70AD. .   God stopped using Israel, and started using the Christian Church, and still IS.  When the fullness of the Gentile is reached, God will Rapture the Christians (the Church) off the surface of the Earth (Revelation 4:1, John is the Church's cruise directer).  God will then call Israel back to full service, per Revelation chapter 7.  God will put a special seal in their foreheads, and they will serve God zealously.

Romans 11 

1 I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin.

2 God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying,

3 Lord, they have killed thy prophets, and digged down thine altars; and I am left alone, and they seek my life.

4 But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal.

5 Even so then at this present time also there is a remnant according to the election of grace.

6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.

7 What then? Israel hath not obtained that which he seeketh for; but the election hath obtained it, and the rest were blinded

8 (According as it is written, God hath given them the spirit of slumber, eyes that they should not see, and ears that they should not hear;) unto this day.

9 And David saith, Let their table be made a snare, and a trap, and a stumblingblock, and a recompence unto them:

10 Let their eyes be darkened, that they may not see, and bow down their back alway.

11 I say then, Have they stumbled that they should fall? God forbid: but rather through their fall salvation is come unto the Gentiles, for to provoke them to jealousy.

12 Now if the fall of them be the riches of the world, and the diminishing of them the riches of the Gentiles; how much more their fulness?

13 For I speak to you Gentiles, inasmuch as I am the apostle of the Gentiles, I magnify mine office:

14 If by any means I may provoke to emulation them which are my flesh, and might save some of them.

15 For if the casting away of them be the reconciling of the world, what shall the receiving of them be, but life from the dead?

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 graffed in among them, and with them partakest 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 graffed in.

20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, 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 also shalt be cut off.

23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.

24 For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree?

25 For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.

26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:

27 For this is my covenant unto them, when I shall take away their sins.

28 As concerning the gospel, they are enemies for your sakes: but as touching the election, they are beloved for the fathers' sakes.

29 For the gifts and calling of God are without repentance.

30 For as ye in times past have not believed God, yet have now obtained mercy through their unbelief:

31 Even so have these also now not believed, that through your mercy they also may obtain mercy.

32 For God hath concluded them all in unbelief, that he might have mercy upon all.

33 O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out!

34 For who hath known the mind of the Lord? or who hath been his counseller?

35 Or who hath first given to him, and it shall be recompensed unto him again?

36 For of him, and through him, and to him, are all things: to whom be glory for ever. Amen.