It's an acknowledgement that one is under the New Covenant. You're drinking from a cup with the symbolic blood of the New Covenant in it. That's a clear indicator of participation.
I disagree
That may be so, but it clearly tells us that the law of the New Covenant is different from the law of the Old Covenant.
How is it different?
The Bible also CLEARLY tells us that BOTH covenants are between God and Israel.
Jer 31:31-33 (AKJV/PCE)
(31:31) ¶ 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: (31:32) 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: (31:33) 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.
I just posted the verse that clearly says exactly that. You already acknowledges that there would be a law written on the hearts of those in the New Covenant, and I just showed that a New Covenant means a New Law, per Hebrews 7.
What wasn't clear, there?
Hebrews is thoroughly HEBREW. Does this cancel Jeremiah 31?
The prophets of Israel explain it all very clearly.
Ezek 36:24-28 (AKJV/PCE)
(36:24) For I will take you from among the heathen, and gather you out of all countries, and will bring you into your own land. (36:25) ¶ Then will I sprinkle clean water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will I cleanse you. (36:26) A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh. (36:27) And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do [them]. (36:28) And ye shall dwell in the land that I gave to your fathers; and ye shall be my people, and I will be your God.
Ezek 37:21-24 (AKJV/PCE)
(37:21) And say unto them, Thus saith the Lord GOD; Behold, I will take the children of Israel from among the heathen, whither they be gone, and will gather them on every side, and bring them into their own land: (37:22) And I will make them one nation in the land upon the mountains of Israel; and one king shall be king to them all: and they shall be no more two nations, neither shall they be divided into two kingdoms any more at all: (37:23) Neither shall they defile themselves any more with their idols, nor with their detestable things, nor with any of their transgressions: but I will save them out of all their dwellingplaces, wherein they have sinned, and will cleanse them: so shall they be my people, and I will be their God. (37:24) And David my servant [shall be] king over them; and they all shall have one shepherd: they shall also walk in my judgments, and observe my statutes, and do them.
Really? Who are the branches that were grafted in when the Jews were broken off, then?
Those broken off were not ALL of the Jews. Gentiles were always allowed to join with Israel, even since the very day God brought them out of Egypt.
Exod 12:43-51 (AKJV/PCE)
(12:43) ¶ And the LORD said unto Moses and Aaron, This [is] the ordinance of the passover: There shall no stranger eat thereof: (12:44) But every man's servant that is bought for money, when thou hast circumcised him, then shall he eat thereof. (12:45) A foreigner and an hired servant shall not eat thereof. (12:46) In one house shall it be eaten; thou shalt not carry forth ought of the flesh abroad out of the house; neither shall ye break a bone thereof. (12:47) All the congregation of Israel shall keep it. (12:48) And when a stranger shall sojourn with thee, and will keep the passover to the LORD, let all his males be circumcised, and then let him come near and keep it; and he shall be as one that is born in the land: for no uncircumcised person shall eat thereof. (12:49) One law shall be to him that is homeborn, and unto the stranger that sojourneth among you. (12:50) Thus did all the children of Israel; as the LORD commanded Moses and Aaron, so did they. (12:51) And it came to pass the selfsame day, [that] the LORD did bring the children of Israel out of the land of Egypt by their armies.
You aren't. You're giving evidence that supports my side.
Believe whatever you want.