Opponents of the fulfilled view will cling to this passage and say "See! It says that God is going to make a New Covenant with His people, Israel in our future!! It's right there plain as day!!"
The passage says...
“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 not according to the covenant that I made with their fathers in the day that I took them by the hand to lead them out of the land of Egypt, My covenant which they broke, though I was a husband to them,says the Lord. But this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people." Jeremiah 31:31-33
Now again, this confusion boils down to failing to see the clear fulfillment of this passage in the New Testament. We have here Jeremiah writing sometime hundreds of years prior to the days of Christ. He predicts a time in the future when God would save a remnant of Israel and would establish a New Covenant with them.
Centuries pass, the last days arrive, Christ arrives and dies on the cross, ascends to heaven, and the apostolic period begins.
Now the author of Hebrews around AD65 or so, (hundreds of years after Jeremiah) comes and writes Hebrews.
In Hebrews he speaks of many things regarding the Old Covenant which was flawed and was only temporary and which was inferior.
He writes also about the New Covenant which was in the "already but not yet" phase at this point. Remember, it couldn't fully be brought in until the former things were thrown down- the temple, alter, etc. This would happen at the destruction of Jerusalem a short time after the author wrote Hebrews.
But look at how the author basically lays this out on a silver platter for us. He is basically interpreting the passage from Jeremiah for us and saying "Here you go guys, this is Jeremiah's prediction being fulfilled right now!" He writes...
"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...
For if that first covenant had been faultless, then no place would have been sought for a second. Because finding fault with them, He says:
(now here is when the author begins quoting Jeremiah).....
“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 not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the Lord. For this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people....
In that He says, “A new covenant,” He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away." Hebrews 8:6-13
Do you understand what he did there? He is speaking of the Covenant that was "becoming obsolete and growing old and ready to vanish away". He is applying Jeremiah's passage to HIS DAY. Not our day.
And ironically enough, Jeremiah later in that same passage and the author of Hebrews in that same passage say...
"For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more."
Sounds a lot like forgiveness in Christ to me!