Heb 8:6-10
6But now hath he obtained a more excellent ministry, by how much also he is the mediator of a better covenant, which was established upon better promises.
7For if that first covenant had been faultless, then should no place have been sought for the second.
8For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
9Not 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 continued not in my covenant, and I regarded them not, saith the Lord.
10For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
11And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest.
12For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
13In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away.
What is the old covenant? and what is the new covenant? The old covenant or the first covenant which was made, was made by the Israelites to Yahweh at Mount Sinai, when the Israelites said all you say we will do... Deut 5:27
This represents the first covenant by the people to Yahweh. It was the PEOPLE who promised Yahweh and made a covenant with Yahweh to do all Yahweh says. However they soon forgot their promise and when Moshe (Moses) went up to the mountain to get the two tablets, they got impatient and promptly broke all the ten commandments.
Therefore the bible says in Heb 8:7, about the first covenant not being faultless, hence the need for a second covenant. Because the first covenant was that which the Israelites made with Yahweh and it is not referring to the law. That is why it says in verse 8, for finding fault with them, Yahweh will make a new covenant with the house of Israel and the house of Judah...
This the new covenant that the laws of Yahweh will be put into the Israelites minds and be written on their hearts.
In the old covenant, it was the people who said, all that Yahweh says we will do and it was written on stone. But in the new covenant, Yahweh said I will and it is written on the heart and in the mind.
But it is still the same law that is written on the hearts and in the minds of the house of Israel. Not only the letter is kept, but also the spirit of the law.
Notice also that this new covenant is made with the house of Israel, and no where can it be found in the bible that Yahweh makes any covenant with the gentiles. So then how do the gentile christians get the surety of this new covenant?