Through the words of Jeremiah, to whom did God give this promise to?
Jeremiah 31:31 “Behold, the days are coming, declares the Lord, when I will make a new covenant with the house of Israel and the house of Judah,32 not like the covenant that I made with their fathers on the day when I took them by the hand to bring them out of the land of Egypt, my covenant that they broke, though I was their husband, declares the Lord.33 For this is the covenant that I will make with the house of Israel after those days, declares the Lord: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people.34 And no longer shall each one teach his neighbor and each his brother, saying, ‘Know the Lord,’ for they shall all know me, from the least of them to the greatest, declares the Lord. For I will forgive their iniquity, and I will remember their sin no more.”
It was to Israel and Judah, and yet we claim these for the Church, and even Gentiles.
Paul verifies this several times:
1 Corinthians 11:25 In the same way also he took the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.”26 For as often as you eat this bread and drink the cup, you proclaim the Lord's death until he comes.
2 Corinthians 3:4 Such is the confidence that we have through Christ toward God. 5 Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, 6 who has made us sufficient to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life.
7 Now if the ministry of death, carved in letters on stone, came with such glory that the Israelites could not gaze at Moses' face because of its glory, which was being brought to an end, 8 will not the ministry of the Spirit have even more glory? 9 For if there was glory in the ministry of condemnation, the ministry of righteousness must far exceed it in glory.10 Indeed, in this case, what once had glory has come to have no glory at all, because of the glory that surpasses it. 11 For if what was being brought to an end came with glory, much more will what is permanent have glory.
12 Since we have such a hope, we are very bold, 13 not like Moses, who would put a veil over his face so that the Israelites might not gaze at the outcome of what was being brought to an end. 14 But their minds were hardened. For to this day, when they read the old covenant, that same veil remains unlifted, because only through Christ is it taken away. 15 Yes, to this day whenever Moses is read a veil lies over their hearts. 16 But when one[c] turns to the Lord, the veil is removed. 17 Now the Lord[d] is the Spirit, and where the Spirit of the Lord is, there is freedom. 18 And we all, with unveiled face, beholding the glory of the Lord,[e] are being transformed into the same image from one degree of glory to another. For this comes from the Lord who is the Spirit.
And the writer of Hebrews affirms this 3 more times.
If this prophecy is fulfilled in the Church, how can we separate the Church from Judah and Israel?
Continuity is clear.