The New Testament invariably sets before Christians the gospel of grace and faith in Christ as He is revealed in that gospel. On that basis it calls believers to obey God. We live by faith. That simply means that what we believe concerning Christ and our position in Him governs what we do. We respond to God’s word and God’s law in the light of the cross. Calvary controls our response to Sinai.
Any attempt to set up a system of rules or principles in the place of a life lived by faith in Christ will bring bondage and bitterness. C. H. Spurgeon’s comment (on Psalm 37:31) about God’s law is memorable: “In the head it puzzles, on the back it burdens, in the heart it upholds.” Believers keep God’s law because they love it and the One who gave it, the One who in love for them gave His Son to be their Saviour. The gospel motivates believers to observe God’s law as a delight to their soul, an expression of the very will of God they find written on their hearts. The law may tell us what to do, but it cannot give us the desire or power to do it. Only gospel grace can do that. To divorce obedience from the gospel and from Christ is blatant legalism. It is an unlawful use of God’s law.
A common sin unites all these abuses. Ultimately, each of them substitutes the law for Christ. Christ, not the law, should be for us the way of salvation, the base of all our operations, the ground of our freedom from condemnation, and the source of our motivation and power to live holy lives. We must never allow anyone to set the law in Christ’s place.
Let the weight of the law fall on sinners. God intends that it should. He did not give it to bear down on His redeemed people, because it has already fallen in all its force on their Saviour and Substitute. Did not Christ perfectly fulfil the law for His people? Did He not then go to the cross and pay the full penalty for all their breaches of the law? If the law lay hard on Christ—if it bore down on Him—and He satisfied it, then it is unlawful for any man to make it bear down on a believer in Christ.
We must ever be watchful lest anyone move us from the lawful to the unlawful use of God’s law.*
*Cairns, A. (2000). Chariots of God: God’s Law in Relation to the Cross and the Christian (66–67). Greenville, SC; Belfast, Northern Ireland: Ambassador-Emerald International.