Here are some notes from Bob Felts, who did a great job describing why law came.
What is the purpose of the Law?
God gave the Law to Israel for several reasons.
First, the Law was given to show God's standards of conduct. Those who measure up though obedience to these standards are said to be righteous, while those who do not measure up because of disobedience to the Law are said to be unrighteous.
If we diligently observe this entire commandment before the LORD our God, as he has commanded us, we will be in the right. [Dt 6:25]
Second, the law was given to make us aware of sin. In
Romans 3:20b, Paul wrote:
...for through the law comes the knowledge of sin.
Paul repeats this idea in
Romans 7:7:
...Yet, if it had not been for the law, I would not have known sin. I would not have known what it is to covet if the law had not said, "You shall not covet."
Third, the law was given to make sin increase. This is a concept which many find difficult to believe, because we think that the purpose of law is to cut down on sin. Our societies are based on the assumption that law makes man behave. Yet the Bible is clear that the exact opposite is true -- the Law makes man misbehave. In
Romans 5:20 Paul wrote:
But law came in, with the result that the trespass multiplied; but where sin increased, grace abounded all the more...
And again, Paul repeats this idea in
Romans 7:13:
.... It was sin, working death in me through what is good (the Law), in order that sin might be shown to be sin, and through the commandment might become sinful beyond measure.
When God gave the Law, sin increased. The reason for this is simple. Sin is that which is at enmity with God. In the presence of God's requirements sin reacts to fight against them with the result that we do those things, whether in thought, word, or deed, which are contrary to God. This is why, in
1 Cor 15:56, Paul stated:
...the power of sin is the law.
Sin "feeds" on law (any law -- not just "the Law"). Our will power can suppress some of the tendency of sin, but even the strongest cannot prevail against the power of sin.
Fourth, the Law was given to lead us to Christ.
So the law was put in charge to lead us to Christ that we might be justified by faith.
(
Gal 3:24, NASB)
Given the knowledge of sin in our lives, and given the power of sin in our lives, the only hope for us is not more Law, but the destruction of sin through the Lord Jesus Christ.