There are two way to interpret scripture using scriptural terms. One is to suggest that the apostles ignored the scriptural definitions for words. This is highly unlikely since they quoted and expected one to understand the context of quotes quite often. Even Christ quoted from the older writings and expected one to understand the context.
The better idea is to look at all quotes and word usage in light of the old testament usage. For example here is 1 Peter 2:9-10.
“But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light: Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.”
This well known and very abused verse is well defined by scripture. The following terms must be understood with scripture’s definitions.
Find the definitions for each of the following and you will understand who is the subject of these verses. chosen generation, a royal priesthood, an holy nation, a peculiar people, “not a people” and “have not been shown mercy”.
Chosen or Elect. They both have the same Greek word source.
1 Chronicles 16:13 “O ye seed of Israel his servant, ye children of Jacob, his chosen ones.”
Isaiah 45:4 “For Jacob my servant’s sake, and Israel mine elect, I have even called thee by thy name: I have surnamed thee, though thou hast not known me.”
Royal Priesthood and a Holy Nation.
Exodus 19:6 “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.”
Peculiar People (Peculiar Treasure and Special People).
Exodus 19:5 “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”.
Deuteronomy 14:2 “For thou art an holy people unto Yahweh thy God, and Yahweh hath chosen thee to be a peculiar people unto himself, above all the nations that are upon the earth.”
Deuteronomy 26:18 “And Yahweh hath avouched thee this day to be his peculiar people, as he hath promised thee, and that thou shouldest keep all his commandments”.
Not a people.
Hosea 1:8 “Now when she had weaned Loruhamah, she conceived, and bare a son. Then said God, Call his name Loammi: for ye are not my people, and I will not be your God.”
Have not been shown mercy.
Hosea 1:6 “And she conceived again, and bare a daughter. And God said unto him, Call her name Loruhamah: for I will no more have mercy upon the house of Israel; but I will utterly take them away.”
After a chapter of explaining all the punishment, then God shows how he will allure Israel to Him again.
Hosea 2:23 “And I will sow her unto me in the earth; and I will have mercy upon her that had not obtained mercy; and I will say to them which were not my people, Thou art my people; and they shall say, Thou art my God.”
It should be rather clear that it is true Israel who is the context for 1 Peter 2:9-10. To suggest that Peter, Paul and James for examples had no clue that God had changed His plans puts doubt on the inspiration of scripture. It also destroys many old testament prophecies and promises and makes God a promise breaker.
The modern day Jews are not Israel. Believe the scripture, question the world.