The gentiles are in a different position in regard to their relationship to God. than the Jews. The Jews, as a nation were in a covenant relationship to God. They were offered a covenant by God through Moses, the mediator when they had been delivered from Egyptian bondage. Ex. 19:3-8
3* And Moses went up unto God, and the LORD called unto him out of the mountain, saying, Thus shalt thou say to the house of Jacob, and tell the children of Israel;
4* Ye have seen what I did unto the Egyptians, and how I bare you on eagles’ wings, and brought you unto myself.
5* Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine:
6* And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.
7* And Moses came and called for the elders of the people, and laid before their faces all these words which the LORD commanded him.
8* And all the people answered together, and said, All that the LORD hath spoken we will do. And Moses returned the words of the people unto the LORD.
In Deuteronomy 7, verses 6 to 8 Moses explains God’s reasons for the Law Covenant being given to the nation of Israel.
6* For thou art an holy people unto the LORD thy God: the LORD thy God hath chosen thee to be a special people unto himself, above all people that are upon the face of the earth.
7* The LORD did not set his love upon you, nor choose you, because ye were more in number than any people; for ye were the fewest of all people:
8* But because the LORD loved you, and because he would keep the oath which he had sworn unto your fathers, hath the LORD brought you out with a mighty hand, and redeemed you out of the house of bondmen, from the hand of Pharaoh king of Egypt.
The prophet Amos tells us that this arrangement between God and the Jewish nation was exclusive and excluded all the gentiles. Amos 3:2 You only have I known of all the families of the earth.
In view of these Scriptures we can easily understand why the Jews developed a sense of superiority toward the rest of mankind.
When Jesus came to his people and they refused to accept him as their Messiah, God cast off the Jewish nation and turned to the gentiles to offer the opportunity to become members of Jesus’ bride, those who would be associated with him in the reawakening and restoration of mankind to perfection.
The difference of God’s dealing with the Gentiles as compared to His dealings with the Jews is that in the case of the gentiles, they are not accepted as a nation or a group, but are recognized on an individual basis as the Apostle Paul explains in Romans 12:1-2 and Romans 6:3.
Ro 12:1* I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
Ro 12:2* And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
Ro 6:3* Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?
Ro 6:4* Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Ro 6:5* For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
Because of the plain statement of Scripture that there is no way for anyone to ultimately receive salvation except through acceptance of Jesus as their Savior, many Christians have taken the attitude of exclusiveness that the Jews have. They fail to understand that the time for acceptance of Christ for the vast majority of mankind will be during His millennial kingdom.
As to your second question we should not think that God has barred all Jews from the high calling, but that their acceptance is just like the gentiles, on an individual basis.
God offers the opportunity for the high calling to a few of the human race because it will glorify him most when He has accomplished his great plan of salvation and used the lowest of his intelligent creation in cooperation with His only begotten son to bring all of the human race to perfection.