Christian Apologetics & Research Ministry (CARM) briefly explains the law:
The Law is God’s instructions concerning the moral, social, and spiritual behavior of His people found in the first five books of the Bible. The Law is the very reflection of the nature of God because God speaks out of the abundance of what is in Him. Therefore, since God is pure, the Law is pure. Since God is holy, the Law is holy. The Law consists of the 10 commandments (Exodus 20), rules for social life (Exodus 21-23), and rules for the worship of God (Exodus 25-31). It .. is unable to deliver us into eternal fellowship with the Lord because of Man’s inability to keep it. The Law is a difficult taskmaster because it requires that we maintain a perfect standard of moral behavior. And then when we fail, the Law condemns us to death. We deserve death even if we fail to keep just one point of the law: “For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all” (James 2:10).
A lawyer asked Jesus, “What is the greatest commandment?” Jesus says, “You shall love the Lord your God with all your heart and with all your soul and with all your mind. 38 This is the great and first commandment. 39 And a second is like it: You shall love your neighbor as yourself. 40 On these two commandments depend all the Law and the Prophets.”
The whole of the law hangs upon loving God with ALL my being AND loving others as myself? I don’t know about you, but I can’t fulfill loving God with ALL my being and loving others as myself. If anyone reading this can do this, please show me how! Do you not feel the weight of the law? The weight of the law is astronomically heavy!
Paul says in Romans 5:20, “Now the law came in to increase the trespass, but where sin increased, grace abounded all the more,”
Romans 2:13 says “For it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified.”
But then Christ Himself says, “17Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18 For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished. 19 Therefore whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever does them and teaches them will be called great in the kingdom of heaven. 20 For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven” (Matthew 5:17-20).
In effect the Gospel (the Person and Work of Jesus) says, “Do not worry. I have already fulfilled the law for you in your place. Go, do the law as worship to me.” (My wording)
So what are the implications of Christ fulfilling the law? Christ’s fulfilling the law does not eleviate our requirement to do it, but Christ’s fulfilling the law changes our motivation for doing it.
For instance Ephesians 6:1 says, “Children, obey your parents in the Lord, for this is right.” It does not say, “Children obey your parents for this is right.” There is a paradigm shift in the motivation. When Paul says, “Children obey your parents in the Lord, for this is right”, he’s essentially saying, “Children obey your parents as worship, not to your parents, but to your God, for this is right.” Otherwise “obey your parents for this is right” is a command to fulfill the law. But to “obey your parents in the Lord for this is right” is to obey the law of Christ.
1 Corinthians 10:31 says, “So, whether you eat or drink, or whatever you do, do all to the glory of God.” How is this fulfilled other than as I take a bite of my food I do it as worship to my God for giving this good gift to me? And how is Christ’s fulfilling the law for me and in my place change my life?
If Christ really did fulfill 100% of the law, then as I put my faith in Him, I am free from the weight of fulfilling it. It does not eleviate me doing it, but it takes away the weight of fulfilling it.
Biblically, I am required to love my wife (Ephesians 5:33). Let’s say I bought some flowers and presented them to her. As she says, “Thank you! They are beautiful!”, I respond, “It was my duty.” If I have no delight in presenting the flowers, I might as well only try fulfilling the law.
Take the same action, but this time I have delight in presenting the flowers. I have joy in presenting the flowers. When she says, “Thank you! They’re beautiful!”, I would then respond, “It is my pleasure!”
There is a paradigm shift in the reason behind the same action. We can take the same idea and look at the law in this fashion. Christ fulfilled 100% of the law. Doing anything in hope to repay my sin has no effect. But if I delight to do the law because of what Jesus has done for me, then it becomes a sweet smelling savor to our Christ.