Rom.11:  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.
 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:
 For this is my covenant unto them, when I shall take away their sins.
 As concerning the gospel, they are enemies for your sakes: but as touching the election, they are beloved for the fathers’ sakes.
 For the gifts and calling of God are without repentance.
The gifts and calling of the Jews has not been forgotten by God neither has He repented of their choosing. He promised centuries ago to make a new covenant with them and God is not slack concerning His promises but rather wants not only the Jews but ALL men Jew and Gentile to come to repentance but there is coming a time when the mysteries of the church will reach a termination point and the fullness of the Gentiles will be harvested. We Christians refer to this event as the Rapture. When the mysteries have come to full fruition the mystery of the return of Israel will begin to unfold.
God promised this in Jeremiah chapter 31.
Jeremiah 31:  Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah:
 Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD:
 But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
 And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD; for I will forgive their iniquity, and I will remember their sin no more.
 Thus saith the LORD, which giveth the sun for a light by day, and the ordinances of the moon and of the stars for a light by night, which divideth the sea when the waves thereof roar; The LORD of hosts is his name:
 If those ordinances depart from before me, saith the LORD, then the seed of Israel also shall cease from being a nation before me for ever.
 Thus saith the LORD; If heaven above can be measured, and the foundations of the earth searched out beneath, I will also cast off all the seed of Israel for all that they have done, saith the LORD.
 Behold, the days come, saith the LORD, that the city shall be built to the LORD from the tower of Hananeel unto the gate of the corner.
 And the measuring line shall yet go forth over against it upon the hill Gareb, and shall compass about to Goath.
 And the whole valley of the dead bodies, and of the ashes, and all the fields unto the brook of Kidron, unto the corner of the horse gate toward the east, shall be holy unto the LORD; it shall not be plucked up, nor thrown down any more for ever.
The promises will be fulfilled in a period of time which God calls “after those days”. In Romans we are told they will be fulfilled AFTER the harvesting of the Gentiles. This clearly indicates the “after those days” is speaking of the calling out of a body of Gentile believers before the fulfillment of the promise to the houses of Israel. Look in Acts 15. We find a great discussion over 1) whether Gentiles may be saved and 2) if so, must they keep the law of Moses in order to be saved.
Acts.15: And when there had been much disputing, Peter rose up, and said unto them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe.
 And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
 And put no difference between us and them, purifying their hearts by faith.
 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?
 But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they.
 Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles and wonders God had wrought among the Gentiles by them.
 And after they had held their peace, James answered, saying, Men and brethren, hearken unto me:
 Simeon hath declared how God at the first did visit the Gentiles, to take out of them a people for his name.
 And to this agree the words of the prophets; as it is written,
 After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up:
 That the residue of men might seek after the Lord, and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things.
 Known unto God are all his works from the beginning of the world.
 Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
Here clearly we are told the new covenant will occur AFTER the time of the Gentiles being called by faith. We are told in the passage as a proof Gentiles can be saved the prophets spoke of the saving of Israel and new covenant occurring after the saving of the Gentile through faith. Before the return of the Lord there must needs be a Gentile body saved first. (verses 13-18)
The book of Hebrews attests to this as well for we find in Hebrews 8:
Heb.8:  For if that first covenant had been faultless, then should no place have been sought for the second.
 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord.
 For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
 And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest.
 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
 In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away.
Again the new covenant will be after those days and it is not a matter of Jews believing but simply by existing upon the return of the Lord. If they endure to the end of the Tribulation God has promised to make a new covenant with them. One in which He removes their sins and places His law in their hearts. It will usher in the Millennial Reign of Christ. What other time past or future has it been utterly unnecessary to teach about the Lord? When has all of mankind known Him? Only when He physically sits on a throne in Jerusalem and all of the world will be subject to Him as King of Kings and Lord of Lords.
This promise is reiterated in Hebrews chapter 10:
Heb.10: This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;
 And their sins and iniquities will I remember no more.
In conclusion the mysteries of the Gentile Age and the Church Age will come to an end when the body of believers are removed. At this time, the nation of Israel will once again seek their God and God will hear their cry. The mystery of iniquity will be full accomplished and Jesus Christ will return to destroy the anti-Christ and establish His kingdom on earth with Jerusalem the capital of the world.