There can never be any question as to whether the Messiah was ever on Earth and no question as to who the Messiah is when he arrives on Earth. There will be signs that cannot be denied when the Messiah arrives. Because In that day no one will need to look in any book, neither a 'New Testament,' nor even the Hebrew Scriptures, to tell them what is Right and what is Wrong. They will know it instinctively because it will be in their hearts, truly making G-d their G-d, and in turn, truly making them G-d's People. Certainly this has not happened yet, and so this passage in Jeremiah 31:31-32 cannot be referring to the New Testament.

The scripture that reveals the truth is in Yirmiyahu - Jeremiah and many more books of the Tanakh. Let us take a look at

Yirmiyahu - Jeremiah - Chapter 31

30 Behold, days are coming, says the Lord, and I will form a covenant with the house of Israel and with the house of Judah, a new covenant.

31 Not like the covenant that I formed with their forefathers on the day I took them by the hand to take them out of the land of Egypt, that they broke My covenant, although I was a lord over them, says the Lord.

Notice that the verse starts out with “Behold, days are coming, says the Lord” This is considered a prophecy because of the first words of the verse, “Behold, days are coming, says the Lord.”  However, immediately before these few verses that begin with verse 30, there are additional verses that also begin the exact same way, with the words, “Behold, days are coming, says the Lord.” The whole prophecy actually begins with verse 26. As you will read, when one looks at the whole prophecy of Jeremiah 31:26-34, this passage could not be referring to a Messiah that has already been on Earth and left without completing his mission. Here is the whole passage:

Yirmiyahu - Jeremiah - Chapter 31

26 Behold days are coming, says the Lord, and I will sow the house of Israel and the house of Judah with seed of man and seed of beasts.

27 And it shall be, as I have watched over them to uproot and to break down, to demolish and to destroy and to afflict, so will I watch over them to build and to plant, says the Lord.

28 In those days, they shall no longer say, "Fathers have eaten unripe grapes, and the teeth of the children shall be set on edge."

29 But each man shall die for his iniquity; whoever eats the unripe grapes- his teeth shall be set on edge

30 Behold, days are coming, says the Lord, and I will form a covenant with the house of Israel and with the house of Judah, a new covenant.

31 Not like the covenant that I formed with their forefathers on the day I took them by the hand to take them out of the land of Egypt, that they broke My covenant, although I was a lord over them, says the Lord.

32 For this is the covenant that I will form with the house of Israel after those days, says the Lord: I will place My law in their midst and I will inscribe it upon their hearts, and I will be their God and they shall be My people

33 And no longer shall one teach his neighbor or [shall] one [teach] his brother, saying, "Know the Lord," for they shall all know Me from their smallest to their greatest, says the Lord, for I will forgive their iniquity and their sin I will no longer remember

34 So said the Lord, Who gives the sun to illuminate by day, the laws of the moon and the stars to illuminate at night, Who stirs up the sea and its waves roar, the Lord of Hosts is His name.

These verses are, indeed, speaking of the Messianic age, however, they are not speaking of a messiah that has come and gone without completing his mission.

Verse 26 speaks of a time when the House of Israel is reunited with the House of Judah, and when they increase in size as well as in resources.

26 Behold days are coming, says the Lord, and I will sow the house of Israel and the house of Judah with seed of man and seed of beasts. [Jeremiah 31:26]

Then G-d states that just as He watched over the Jews when He saw fit to punish them, so, too, will He continue to watch over the Jews as everything gets better:

27 And it shall be, as I have watched over them to uproot and to break down, to demolish and to destroy and to afflict, so will I watch over them to build and to plant, says the Lord [Jeremiah 31:28]

We will know that messiah has arrived when the House of Judah and the House of Israel has reunited. And there are more signs, as we shall see.

The next verses actually deny that any messiah can die for our sins:

[Jeremiah 31:28-29]

28 In those days, they shall no longer say, "Fathers have eaten unripe grapes, and the teeth of the children shall be set on edge."

29 But each man shall die for his iniquity; whoever eats the unripe grapes- his teeth shall be set on edge

Verses 28-29 above are saying that in this future time, no one will continue to believe that one person can die and thereby take away the guilt for another person's sins. Jeremiah is saying that when those days come, all will recognize, as the Bible has said repeatedly (See Exodus 32:30-35; Deuteronomy 24:16; and Ezekiel 18:1-4) that the person who sins will always be the only one who gets the punishment for that sin. This is what it states quite simply in Deuteronomy 24:16, No man shall be put to death for the sins of his children, no child will be put to death for the sins of his father. Every man shall be put to death for his own sin.

This description of this messianic age continues with Jeremiah 31:30, which is the passage that is usually quoted without the verses that come before it. Just a simple overview of these verses indicates that what it describes has not happened yet.

The first verse of the passage reads:

30 Behold, days are coming, says the Lord, and I will form a covenant with the house of Israel and with the house of Judah, a new covenant.

However, the House of Israel, which was made up of the Ten Lost Tribes, have been lost and scattered around the world since the fall of the Northern Kingdom around 721 B.C.E.. The House of Israel, the Ten Lost Tribes, cannot be re-united with the House of Jacob, because the House of Israel has not been around for thousands of years, that is why they are called the Ten LOST Tribes. This passage in Jeremiah is describing a Jewish People where all of the descendants of every tribe thrives, and has made their way to the Promised Land. Because it speaks of both the House of Israel and the House of Judah together, with G-d, in a single new covenant, and since the House of Israel cannot be unified with the House of Judah,

The Jews are too comfortable in their Diaspora, and so for this prophecy to become reality ALL JEWS MUST return to the holy land of Israel. G-d works in mysterious ways so to get the Jews to return to Israel he makes them uncomfortable by causing anti-Semitism, and we are now seeing this in Europe, especially in France where many Jews are making aliyah in masse to the holy land of Israel. But all Jews must return, so we are seeing this anti-Semitism grow and spread. When all Jews have returned to the Promised Land, they will eventually form into their perspective tribes, thus fulfilling this prophecy.  There is some debate about forming into their perspective tribes;

Rabbi Akiva says, “The ten tribes will not return, as the verse says (Deuteronomy 29:27), ‘And the L‑rd uprooted them from upon their land, with fury, anger and great wrath, and He cast them to another land, as it is this day.’ Just as a day passes and it will never return, so too, they will be exiled never to return.”

Rabbi Eliezer says, “Just like a day is followed by darkness, and the light later returns, so too, although it will become ‘dark’ for the ten tribes, G‑d will ultimately take them out of their darkness.”

The Talmud then goes on to cite a third opinion:

Rabbi Shimon ben Yehudah, of the town of Acco, says in the name of Rabbi Shimon: “If their deeds are as this day’s, they will not return; otherwise they shall.”

So, in short, there seem to be three opinions on the matter. Rabbi Akiva holds that the ten tribes are not coming back; Rabbi Eliezer holds that they are; and Rabbi Shimon says that it depends on whether they repent.

In my opinion I think they will reunite.

There is another reference, also in Jeremiah, in the 23rd chapter that describes the same thing, where all the Jews have returned to the Promised Land, and which also begins with the same words found in Jeremiah 31:26 and 31:30

Yirmiyahu - Jeremiah - Chapter 23

5 Behold, days are coming, says the Lord, when I will set up of David a righteous shoot, and he shall reign a king and prosper, and he shall perform judgment and righteousness in the land

6 In his days, Judah shall be saved and Israel shall dwell safely, and this is his name that he shall be called, The Lord is our righteousness.

7 Therefore, behold days are coming, says the Lord, when they shall no longer say, "As the Lord lives, Who brought up the children of Israel from the land of Egypt,"

8 But, "As the Lord lives, Who brought up and Who brought the seed of the house of Israel from the northland and from all the lands where I have driven them, and they shall dwell on their land."

This leads us, now, to look at the next two verses of our passage:

31 Not like the covenant that I formed with their forefathers on the day I took them by the hand to take them out of the land of Egypt, that they broke My covenant, although I was a lord over them, says the Lord.

32 For this is the covenant that I will form with the house of Israel after those days, says the Lord: I will place My law in their midst and I will inscribe it upon their hearts, and I will be their God and they shall be My people [Jeremiah 31:31-32]

What these verses are saying is that everyone will no longer need to look in any book, neither a 'New Testament,' nor even the Hebrew Scriptures, to tell them what is Right and what is Wrong. They will know it instinctively because it will be in their hearts, truly making G-d their G-d, and in turn, truly making them G-d's People. Certainly this has also not happened yet, and so this passage cannot be referring to the New Testament.

What, precisely, does it mean to have G-d's Torah written in our innermost parts?

I delight to do thy will, O my God: yea, thy Torah is within my heart. [Psalm 40:8]

Because G-d's Torah is within us, we know what we are to do, and we are happy to do it.

Please also read carefully. Jeremiah 31:32 does not say 'I will put my NEW Torah in their inward parts' It says, 'I will inscribe my Torah upon their hearts.' The laws of G-d do not change or get changed, they are eternal as G-d is Eternal:

Devarim - Deuteronomy - Chapter 29

28 The hidden things belong to the Lord, our God, but the revealed things apply to us and to our children forever: that we must fulfill all the words of this Torah.

Tehillim - Psalms - Chapter 19

8 The law of the Lord is perfect, restoring the soul; the testimony of the Lord is faithful, making the simple one wise

9 The orders of the Lord are upright, causing the heart to rejoice; the commandment of the Lord is clear, enlightening the eyes.

10 The fear of the Lord is pure, existing forever; the judgments of the Lord are true, altogether just.

Tehillim - Psalms - Chapter 111

7 The works of His hands are truth and justice; all His commandments are faithful.

8 Steadfast forever, made in truth and uprightness

As a matter of fact, Ezekiel 11:17-20 reflects the ideas found in Jeremiah 31:26-34: that G-d's laws will be in our hearts, not books, in the messianic age, which will last forever:

Therefore say, Thus saith the Etrnl G-d; I will even gather you from the people, and assemble you out of the countries where ye have been scattered, and I will give you the land of Israel. And they shall come thither, and they shall take away all the detestable things thereof and all the abominations thereof from thence. And I will give them one heart, and I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh: That they may walk in my statutes, and keep mine ordinances, and do them: and they shall be my people, and I will be their G-d. [Ezekiel 11:17-20]

As I wrote above, this new covenant that G-d speaks about in Jeremiah 31 is not talking about a new covenant, a new contract, and He does not mean a new set of laws, a new Torah, a new scripture. It means the covenant between G-d and the Jews and the laws of that covenant are eternal.

Finally, the text from Jeremiah 31 reads,

33 And no longer shall one teach his neighbor or [shall] one [teach] his brother, saying, "Know the Lord," for they shall all know Me from their smallest to their greatest, says the Lord, for I will forgive their iniquity and their sin I will no longer remember [Jeremiah 31:33]

This new covenant means that no one will have say 'Know the L-rd,' because the whole world will already believe in G-d. This part of the passage especially has not happened yet, and this is proven because had it already happened, no one will have to missionize anyone! Since they spend hundreds of millions of dollars every year, just to missionize the Jews, just to get the Jews to 'Know the L-rd,' then this prophecy in Jeremiah 31 has not happened yet, and these missionaries prove it every day.