Based on Greg Bahnsen’s “By This Standard,” (1991).
- So, what can’t the law do?
a)…The law cannot contribute anything towards the personal justification of one who stands under its curse for violating its precepts. Before the standard of God’s law the sinner will always stand condemned rather than being judged righteous. “By the works of the law shall no flesh be justified in His sight” (Ro.3:20).
Those who hope to find acceptance with God on the basis of their own good deeds cannot find His favour. “You have been discharged from Christ whosoever of you are justified by law; you have fallen away from grace” (Gal.5:4). The very attempt to gain justification in this manner is futile, for “a man is not justified by the works of the law but through faith in Jesus Christ” (Gal.2:16).
b) The law cannot break the stranglehold and power of sin in a person’s life. The principle of Christ’s life-giving Spirit set Paul free from the principle of sin and death… The law of God simply could never overthrow this sinful nature and bring about conformation to its pattern of righteousness. The law could not empower obedience and put a decisive end to the power of disobedience.
The law could show what was right, but the faulty character of the sinner prevented the right from being performed. In the face of this failing, the law was helpless to amend the situation…We must ever remember that the law is a pattern only; it cannot supply the power to follow the pattern.
Paul elsewhere expressed this truth by saying, “You are not under law, but under grace” (Ro.6:14). The person who is “under law” is one whose resources and powers are determined exclusively by the law. The context of Paul’s declaration is the key to understanding it correctly. Being “under law” takes a parallel position to having sin reign within oneself (v.12), to sin having dominion over oneself (v.14a), to being a servant of sin (v.17). Instead of being “under law” and by its impotence enslaved to sin, Paul sees the believer as “under grace” instead; that is, under the determining power of God’s merciful and mighty work of salvation. This grace makes one over into a servant of righteousness and obedience (vv.13, 16-18).
…In context it is clear that being under law is a position of powerlessness wherein the bondage to sin remains unbroken, whereas being under grace supplies the spiritual strength to break off from sinning and now to obey the righteous standards of God (found in His law)…
c) The law delivered by Moses never could actually make anything perfect (Heb.7:19). While it beautifully foreshadowed the saving ministry of Jesus Christ in its ceremonial enactments, the law never could by its repeated sacrifices secure the eternal redemption needed by God’s people (Heb. 9:11-12; 10:1-12)… It was “imposed until a time of reformation” (Heb.9:10) (p.184-187).
2) What can the law do?
a) The law declares the character of God and so reveals His glory.
The kind of lifestyle and attitudes which the Lord requires of His people tells us, of course, what kind of God He is. If you wish to see the contrast between the pagan deities and the living and true God of the Bible, simply observe the difference between the things which they command. Moloch demanded child sacrifice, while Jehovah commanded the care and nurture of children, to take one example. Psalm 119 extensively applies the attributes of God (perfection, purity, righteousness) to the precepts of God. Throughout the law God reinforces the authority of His commands by following them with the declaration, “I am the Lord.”
In showing the true and radical demand of the law’s requirements (Mat.5:21-47), Christ was showing us the perfection of God which is desired in us (v.48). John Newton wrote:
When we use the law as a glass to behold the glory of God, we use it lawfully. His glory is eminently revealed in Christ; but much of it is with a special reference to the law, and cannot be otherwise discerned. We see the perfection and excellence of the law in His life. God was glorified by His obedience as a man. What a perfect character did He exhibit! Yet it is no other than a transcript of the law.
b) The law displays the demand of God upon our lives as men.
…Before delivering the summation of the law in the Decalogue, God spoke to Israel with these words: “Now therefore, if you will obey My voice indeed, and keep My covenant, then you shall be My own possession from among all peoples, for all the earth is Mine; and you shall be unto Me a kingdom of priests and a holy nation” (Ex.19:5-6).
Obedience to the law is obedience to the voice of the King, the Lord of the covenant, and as such it shows us what it means to be His subjects and servants. For us to pray “Thy kingdom come,’ is likewise to pray “Thy will be done on earth” (Mat.6:10). And God’s will is communicated by His commandments, telling us what His holiness means on a creaturely level (Lev.20:7-8).
c) The law pronounces blessing upon adherence to its demands.
God’s commandments were laid down for our good (Deut.10:13), and obedience to them is the pure delight of the righteous man (Ps.1:1-2). Such obedience brings prosperity (Ps.1:3-4) and good success (Joshua 1:7). The Lord’s lovingkindness is upon them that keep His precepts (Ps.103:17-18), blessing them and their cultures (cf. Deut.7, 11, 28, 30). Indeed, Paul taught that “godliness is profitable for all things, since it holds promise for the present life and also the life to come” (I Tim.4:8).
Seeking the righteousness of God’s kingdom above all will be rewarded by the supply of every need (Mat.6:33). The law insures that when men are just and righteous, they enjoy the life and blessing which imitation of God constitutes. Thus the commandment was ordained unto life (Ro.7:10), and the man who does the things of the law enjoys life within their sphere (Gal.3:12).
d) The law provides a definition of sin.
By showing us what God is like and what God demands, the law likewise delivers a standard for sin. Sin is lawlessness (I Jn.3:4). In delineating the righteousness which pleases God, the law simultaneously provides the norm of waywardness and rebellion against God. Where there is no law, there can be no transgression (Ro.4:15; 5:13). By the law men come to know what sin is (Ro.3:20; 7:7).
e) The law exposes infractions and convicts of sin.
The law is more than simply an objective code of right and wrong by which, if one is interested, he can judge his performance. The law, being Spiritual (Ro.7:14), is part of that word of God which is living and active-sharper than any two-edged sword, so as to pierce deeply into the recesses of man’s heart and bring to light his darkest character. The law judges the thoughts and intents of the heart (Heb.4:12) and produces a conviction of our sinfulness (for example, Ro.7:9-13) (p.192-195).
 “Letters of John Newton,” 1960, p.47.