“The law cannot do any more in sanctification than it did in justification.”

"God himself did what the law itself could never do. The law commands, but only God can save. This is not just good news for the newly converted, but for the mature believer. As John Murray says, “The law cannot do any more in sanctification than it did in justification.” It is no more the office of the law (even according to its third use) to empower us for holiness than to raise us from the dead and put us right before God in the first place. 

The only source of life and power in the Christian life is the same as it was at the very first: the good news that God has done what the law (and our obedience) could never do.

The only source of life and power in the Christian life is the same as it was at the very first: the good news that God has done what the law (and our obedience) could never do. Thus, we always respond to the law (in its third use) as those who have been saved and are being saved and will be saved according to God’s promise, within a covenant of grace.

. . . we always respond to the law (in its third use) as those who have been saved and are being saved and will be saved according to God’s promise, within a covenant of grace.

Because we are in Christ, God’s law, as the expression of his righteous verdict upon our lives, concurs with the gospel in delivering the judgment, “Not guilty.” And now, acknowledging us to be right before God, that same law charts our course, revealing God’s unchanging will in which he delights more than sacrifice. Forgiveness is great, but obedience is greater. A guilt offering is necessary for the remission of sins, but a thank offering is something that God treasures above all else.

Because we are in Christ, God’s law, as the expression of his righteous verdict upon our lives, concurs with the gospel in delivering the judgment, “Not guilty.”

It is in view of God’s mercies (the indicative) that we offer ourselves as living sacrifices to God (Rom. 12:1–2). So the good news is that if you are in Christ, you are a new creature. The indicative (i.e., the good news of what God has done—“the mercies of God”) drives the imperatives (i.e., the law in its third use). You have not inherited forgiveness and justification by grace only to have your sanctification determined by a covenant of law.

The indicative (i.e., the good news of what God has done—“the mercies of God”) drives the imperatives (i.e., the law in its third use).

The irony is preserved: the law covenant leads to condemnation, while the promise covenant leads to the very obedience that the law requires but could never elicit. On the other hand, if you are living in open rebellion against the promises of God and do not delight in his law inwardly, then the inheritance does not belong to you even if you have been incorporated visibly into the covenant community. The gospel is greater than we ever imagined, and the judgment is severe for those who reject the realities it brings into our lives.

The irony is preserved: the law covenant leads to condemnation, while the promise covenant leads to the very obedience that the law requires but could never elicit.

~Michael Horton, Introducing Covenant Theology, 192.