The New Covenant is made sure by the blood that Jesus shed on Calvary's cross.  That blood which guarantees to Israel its New Covenant also provides for the forgiveness of sins for the believers who comprise the church.  Jesus' payment for sins is more than adequate to pay for the sins of all of all who will believe in Him.  The New Covenant is called "new" in contrast to the covenant with Moses which is called "old" (Jeremiah 31:32; Hebrew 8:6-13  But 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.   7 For if that first covenant had been faultless, then should no place have been sought for the second.   8 For 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:   9 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 continued not in my covenant, and I regarded them not, saith the Lord.   10 For 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:   11 And 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.   12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.   13 In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away.   In this part of the chapter, the apostle illustrates and confirms the superior excellency of the priesthood of Christ above that of Aaron, from the excellency of that covenant, or that dispensation of the covenant of grace, of which Christ was the Mediator: his ministry is more excellent, by how much he is the Mediator of a better covenant. The body and soul too of all divinity (as some observe) consist very much in rightly distinguishing between the two covenants--the covenant of works and the covenant of grace; and between the two dispensations of the covenant of grace--that under the Old Testament and that under the New.

      I. What is here said of the old covenant, or rather of the old dispensation of the covenant of grace: of this it is said,  That it was made with the fathers of the Jewish nation at mount Sinai, and Moses was the Mediator of that covenant, when God took them by the hand, to lead them out of the land of Egypt, which intimates the great affection, condescension, and tender care of God towards them. That this covenant was not found faultless; it was a dispensation of darkness and dread, tending to bondage, and only a schoolmaster to bring us to Christ; it was perfect in its kind, and fitted to answer its end, but very imperfect in comparison of the gospel. That it was not sure or stedfast; for the Jews continued not in that covenant, and the Lord regarded them not. They dealt ungratefully with their God, and cruelly with themselves, and fell under God's displeasure. God will regard those who remain in his covenant, but will reject those who cast away his yoke from them. That it is decayed, grown old, and vanisheth away. It is antiquated, canceled, out of date, of no more use in gospel times than candles are when the sun has risen. Some think the covenant of peculiarity did not quite decay till the destruction of Jerusalem, though it was forfeited at the death of Christ, and was made old, and was now to vanish and perish, and the Levitical priesthood vanished with it.

    What is here said of the New-Testament dispensation, to prove the superior excellency of Christ's ministry. It is said, that it is a better covenant, a more clear and comfortable dispensation and discovery of the grace of God to sinners, bringing in holy light and liberty to the soul. It is without fault, well ordered in all things. It requires nothing but what it promises grace to perform. It accepts of godly sincerity, accounting it gospel perfection. Every transgression does not turn us out of covenant; all is put into a good and safe hand.    

    That it is established upon better promises, more clear and express, more spiritual, more absolute. The promises of spiritual and eternal blessings are in this covenant positive and absolute; the promises of temporal blessings are with a wise and kind proviso, as far as shall be for God's glory and his people's good. This covenant contains in it promises of assistance and acceptance in duty, promises of progress and perseverance in grace and holiness, of bliss and glory in heaven, which were more obscurely shadowed forth by the promises of the land of Canaan, a type of heaven.

   It is a new covenant, even that new covenant that God long ago declared he would make with the house of Israel, that is, all the Israel of God; this was promised in, and accomplished in Christ. This will always be a new covenant, in which all who truly take hold of it shall be always found preserved by the power of God. It is God's covenant; his mercy, love, and grace moved for it; his wisdom devised it; his Son purchased it; his wisdom devised it; his Son purchased it; his Spirit brings souls into it, and builds them up in it.

   The articles of this covenant are very extraordinary, which are sealed between God and his people by baptism and the Lord's supper; whereby they bind themselves to their part, and God assures them he will do his part; and his is the main and principal part, on which his people depend for grace and strength to do theirs. Here, God articles with his people that he will put his laws into their minds and write them in their hearts. He once wrote his laws to them, now he will write his laws in them; that is, he will give them understanding to know and to believe his law; he will give them memories to retain them; he will give them hearts to love them and consciences to recognize them; he will give them courage to profess them and power to put them in practice; the whole habit and frame of their souls shall be a table and transcript of the law of God. This is the foundation of the covenant; and, when this is laid, duty will be done wisely, sincerely, readily, easily, resolutely, constantly, and comfortably.

He articles with them to take them into a near and very honourable relation to himself.

[1.] He will be to them a God; that is, he will be all that to them, and do all that for them, that God can be and do. Nothing more can be said in a thousand volumes than is comprehended in these few words: I will be a God to them. [2.] They shall be to him a people, to love, honour, observe, and obey him in all things; complying with his cautions, conforming to his commands, comporting with his providences, copying out his example, taking complacency in his favour. This those must do and will do who have God for their God; this they are bound to do as their part of the contract; this they shall do, for God will enable them to do it, as an evidence that he is their God and that they are his people; for it is God himself who first founds the relation, and then fills it up with grace suitable and sufficient, and helps them in their measure to fill it up with love and duty; so that God engages both for himself and them.

He articles with them that they shall grow more and more acquainted with their God: They shall all know me from the least to the greatest, insomuch that there shall not be so much need of one neighbour teaching another the knowledge of God. Here observe,

[1.] In the want of better instruction, one neighbour should be teaching another to know the Lord, as they have ability and opportunity for it.

[2.] This private instruction shall not be so necessary under the New Testament as it was under the Old. The old dispensation was shadowy, dark, ritual, and less understood; their priests preached but seldom, and but a few at a time, and the Spirit of God was more sparingly given out. But under the new dispensation there shall be such abundance of public qualified preachers of the gospel, and dispensers of ordinances statedly in the solemn assemblies, and so great a flocking to them, as doves to their windows, and such a plentiful effusion of the Spirit of God to make the ministration of the gospel effectual, that there shall be a mighty increase and spreading of Christian knowledge in persons of all sorts, of each sex, and of all ages. O that this promise might be fulfilled in our days, that the hand of God may be with his ministers, that a great number may believe and be turned to the Lord!

God articles with them about the pardon of their sins, as what always accompanies the true knowledge of God: For I will be merciful to their unrighteousness.

[1.] The freeness of this pardon. It does not result from merit in man, but from mercy in God; he pardons for his own name's sake.

[2.] The fullness of this pardon; it extends to their unrighteousness, sins, and iniquities; to all kinds of sin, to sins highly aggravated.

[3.] The fixedness of this pardon. It is so final and so fixed that God will remember their sins no more; he will not recall his pardon; he will not only forgive their sins, but forget them, treat them as if he had forgotten them. This pardoning mercy is connected with all other spiritual mercies. Unpardoned sin prevents mercy, and pulls down judgments; but the pardon of sin prevents judgment, and opens a wide door to all spiritual blessings; it is the effect of that mercy that is from everlasting, and the earnest of that mercy that shall be to everlasting. This is the excellency of the new dispensation, and these are the articles of it; and therefore we have no reason to repine, but great reason to rejoice that the former dispensation is antiquated and has vanished away.)  because it actually accomplishes what the Mosaic Covenant could only point to, that is, the child of  God living in a manner that is consistent with the character of God.