"The third use of the Law" is a term I had encountered in the past, but hadn't bothered to look up, on the assumption that it was some bit of abstruse, Puritan-era theologizing. Boy, was I ever wrong! It turns out that "the third use of the Law" basically encompasses the whole question of how the Law of God applies to believers—or whether it applies at all.
The Reformers outlined three purposes—or uses—of the Law of God:
- To constrain evil;
- To convict sinners and bring them to repentance; and
- To guide believers in their Christian walk.
(And I receive excellent instruction from my church on sanctification...the fault lay entirely in my overthinking things, or not being able to connect the biblical dots and seeing the rationle behind the Apostles' [not to mention Puritans'!] calls to holiness.)
But Dr. Montgomery lays it all out quite clearly—and briefly. He briefly surveys the swinging pendulum between "justification without sanctification" and "'sanctification' without justification" in the history of Protestantism; the rise of the social gospel and Christian existentialism; and the dead end of the latter movement. All this is presented as a motivation for what follows: a discussion the Reformation-era discernment of the three uses of the Law outlined above.
He then provides an extended quote from Chapter 6 of Horatius Bonar's God's Way of Holiness; and between that quote and his introduction to it, the scales fell from my eyes, by God's grace.
Essentially, the case comes down to this: above all, we are commanded as Christians to love: Love the Lord our God with all our heart, soul, mind, and strength; and love our neighbour as ourself (Matthew 22:34-40). But—and here's the rub—how do we love? The answer is that God has graciously shown us the way to love—the way to fulfill this supreme of all commandments—through His Law as an expression of His will!
And not the letter of the Law—external obedience, though that is important—so much as the spirit of the Law—having it written upon our hearts, by the supreme grace of God (Jeremiah 31:33): hence, Jesus Christ's expounding of the Law (and especially the Ten Commandments) in His Sermon on the Mount.
No, we are no longer enslaved to the Law and no longer cursed by it—for Jesus Christ has borne the curse for us, on the Cross. But we are now at liberty to follow the Law out of love, by the indwelling Holy Spirit.
We are still sinners—simul justus et peccator—and still capable of disobeying God's Law, in which case the only remedy available to us is the same as that for non-believers: repentance and faith in the atoning work of Jesus Christ as our sin-bearer and propitiation. But now, when we do obey God's Law, we should do so not out of fear or a sense of grudging compulsion, but out of love for God, gratitude to Him, and a desire to live out His command to love as He has graciously provided and decreed.
For now, I can only respond by quoting Paul (though admittedly from an entirely different context):
Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!
"For who has known the mind of the Lord,
or who has been his counselor?"
"Or who has given a gift to him
that he might be repaid?"
For from him and through him and to him are all things. To him be glory forever. Amen. (Romans 11:33-36)
Soli Deo Gloria!