Jeremiah predicted that the new covenant would come in the future:
Jer_31:31 "Behold, the days are coming, says the LORD, when I will make a new covenant with the house of Israel and with the house of Judah—
Christ confirmed this new covenant and confirmed that his blood was the agency of this covenant:
Luk_22:20 Likewise He also took the cup after supper, saying, "This cup is the new covenant in My blood, which is shed for you.
Paul knew this and confirms that the new covenant was for the church that was established on Pentecost as seen in Acts 2:
2Co 3:5 Not that we are sufficient of ourselves to think of anything as being from ourselves, but our sufficiency is from God,
2Co 3:6 who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
Paul believed that the church were ministers of the new covenant and saw that the spirit of God, through Christ, was what made the new covenant a better promise...a promise of eternal life:
Heb_8:6 But now He has obtained a more excellent ministry, inasmuch as He is also Mediator of a better covenant, which was established on better promises.
and we know from promises God made to Israel, and not the Church, in the New Covenant that have not yet been fulfilled but which require a literal, functioning nation of Israel for fulfillment, then we know that it is impossible that the Church is Israel.
“A Redeemer will come to Zion, and to those who turn from transgression in Jacob,” declares the LORD. 21 “As for Me, this is My covenant with them,” says the LORD: “My Spirit which is upon you, and My words which I have put in your mouth shall not depart from your mouth, nor from the mouth of your [a]offspring, nor from the mouth of your [b]offspring’s offspring,” says the LORD, “from now and forever.”"“Behold, days are coming,” declares the LORD, “when I will make a new covenant with the house of Israel and with the house of Judah, 32 not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them,” declares the LORD. 33 “But this is the covenant which I will make with the house of Israel after those days,” declares the LORD, “I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people. 34 They will not teach again, each man his neighbor and each man his brother, saying, ‘Know the LORD,’ for they will all know Me, from the least of them to the greatest of them,” declares the LORD, “for I will forgive their iniquity, and their sin I will remember no more.” (Jeremiah 31:31-34)
Has that promise been fulfilled? Do all the Jews, down to the last one, know Jesus Christ? And if it hasn't been fulfilled yet, did God lie when He made that promise to His covenant, chosen people?
How about this promise to Israel?
“My servant David will be king over them, and they will all have one shepherd; and they will walk in My ordinances and keep My statutes and observe them. 25 They will live on the land that I gave to Jacob My servant, in which your fathers lived; and they will live on it, they, and their sons and their sons’ sons, forever; and David My servant will be their prince forever. 26 I will make a covenant of peace with them; it will be an everlasting covenant with them. And I will [b]place them and multiply them, and will set My sanctuary in their midst forever. 27 My dwelling place also will be with them; and I will be their God, and they will be My people. 28 And the nations will know that I am the LORD who sanctifies Israel, when My sanctuary is in their midst forever.”’” (Ezekiel 37:21-28)
Is David currently king over the nation of Israel? Did God lie when He made that promise to the nation of Israel?