For I will be merciful to their unrighteousness - That is, the blessing of "pardon" will be much more richly enjoyed under the new dispensation than it was under the old. This is the "fourth" circumstance adduced in which the new covenant will surpass the old. That was comparatively severe in its inflictions (see Hebrews 10:28); marked every offence with strictness, and employed the language of mercy much less frequently than that of justice. It was a system where law and justice reigned; not where mercy was the crowning and prevalent attribute. It was true that it contemplated pardon, and made arrangements for it; but it is still true that this is much more prominent in the new dispensation than in the old. It is there the leading idea. It is what separates it from all other systems. The entire arrangement is one for the pardon of sin in a manner consistent with the claims of law and justice, and it bestows the benefit of forgiveness in the most ample and perfect manner on all who are interested in the plan. In fact, the uniqueness by which the gospel is distinguished from all other systems, ancient and modern, philosophic and moral, pagan and deistical, is that it is a system making provision for the forgiveness of sin, and actually bestowing pardon on the guilty. This is the center, the crown, the glory of the new dispensation. God is merciful to the unrighteousness of people and their sins are remembered no more.
Will I remember no more - This is evidently spoken after the manner of men, and in accordance with human apprehension. It cannot mean literally that God forgets that people are sinners, but it means that he treats them as if this were forgotten. Their sins are not charged upon them, and they are no more punished than if they had passed entirely out of the recollection. God treats them with just as much kindness, and regards them with as sincere affection, as if their sins ceased wholly to be remembered, or which is the same thing, as if they had never sinned.

I will be merciful to their unrighteousness - In order to be their God, as mentioned under the preceding verse, it is requisite that their iniquity should be pardoned; this is provided for by the immolation of Jesus Christ as the covenant sacrifice. By his blood, redemption has been purchased, and all who with penitent hearts believe on the Lord Jesus receive remission of sins, and God remembers their iniquities no more against them so as to punish them on that account. All spiritual evil against the nature and law of God is represented here under the following terms: -
1. Unrighteousness, αδικια, injustice or wrong. This is against God, his neighbor, and himself.
2. Sin, ἁμαρτια, deviation from the Divine law; Missing the Mark; aiming at happiness but never attaining it, because sought out of God, and in the breach of his laws.
3. Iniquity, ανομια, lawlessness, not having, knowing, or acknowledging, a law; having no law written in their hearts, and restrained by none in the conduct of their lives. All these are to be removed by God's mercy; and this is to be understood of his mercy in Christ Jesus.

For I will be merciful to their unrighteousness,.... That is, sin; for all unrighteousness is sin, being contrary to the justice of God, and his righteous law: and the phrase is expressive of God's forgiveness of it, which is a very considerable article of the covenant of grace; mercy is the spring and original of pardon; it is what God delights in, and therefore he pardons freely; it is large and abundant, and hence he pardons fully; and this lays a foundation for hope in sensible sinners: and the way and means, in and by which God pardons, is the propitiatory sacrifice of his Son; and the word here rendered "merciful", signifies "propitious"; God pardons none but those to whom he is pacified, or rendered propitious by Christ; there is no mercy, nor pardon, but through him; he pardons on the foot of reconciliation and satisfaction for sin by Christ; so that forgiveness of sin is an act of justice, as well as of mercy; or it is an act of mercy streaming through the blood and sacrifice of Christ.
And their sins and their iniquities will I remember no more; by which are meant all kind of sin, original and actual; sins before and after conversion; every sin but that against the Holy Ghost, and that God's covenant people are never guilty of; these God remembers no more; he casts them behind his back, and into the depths of the sea, so that when they are sought for, they shall not be found; God will never charge them with them, or punish them for them: this is another phrase to express the forgiveness of sins, and distinguishes the new covenant from the old one, or the former dispensation; in which, though there were many typical sacrifices, and a typical removal of sin, yet there was a remembrance of it every year.

For, &c.--the third of "the better promises" (Hebrews 8:6). The forgiveness of sins is, and will be, the root of this new state of inward grace and knowledge of the Lord. Sin being abolished, sinners obtain grace.
I will be merciful--Greek, "propitious"; the Hebrew, "salach," is always used of God only in relation to men.
and their iniquities--not found in Vulgate, Syriac, Coptic, and one oldest Greek manuscript; but most oldest manuscripts have the words (compare Hebrews 10:17).
remember no more--Contrast the law, Hebrews 10:3.

For I will justify them, which is the root of all true knowledge of God. This, therefore, is God's method. First, a sinner is pardoned: then he knows God, as gracious and merciful then God's laws are written on his heart: he is God's, and God is his.