What is God’s law? What part does it play in salvation? What part should it play in a Christian’s daily life? Many people inside and outside the church are confused and sometimes plagued by these questions. The Bible gives the clarity.
1 John 4:8 teaches that God is love. Jesus in Matthew 22:36-38 summarizes God’s law saying all people should love God and love people. God’s moral law is simply a revelation of the character of God. God is loving so we should be too.
Genesis 1:26 and Isaiah 43:7 teach that people are made to reflect the glory of God. Exodus 33:18-34:7 shows that God’s glory is primarily “seen” by knowing God’s character. Exodus 20 gives us the Ten Commandments, which are the best summary of God’s law in the Old Testament.
God’s commands to us are not arbitrary but clearly flow from His character and nature. God loves life so we shouldn’t murder. God is faithful so we should be in marriage. God speaks the truth so should we etc…
Romans 1:19; 2:14-15 show that God’s essential law is on the heart of all people, even those who grow up without the Bible. God’s law was originally on Adam and Eve’s heart. That is part of what it means to be made in His image. This is partially how He reveals His image. God is loving, faithful, truthful, etc…. So Adam and Eve were originally loving, faithful, truthful, etc....
God told Adam in the Garden that if he would obey God he would continue to live. God told him not to eat of the tree of the knowledge of good and evil (Genesis 2.) In Genesis 3 Adam ate of that tree and spiritually died. He was cursed by God and banished from the Garden of Eden.
When Adam and Eve first sinned the image of God in them was shattered but not erased. Imagine a full length mirror that has been severely cracked. If you stand in front of it, you can still see your image, though it is very distorted. This is now how all human beings come into the world. 1 Kings 8:46, 2 Chronicles 6:36, Psalm 51:5 and Romans 3:23, 5:12 all teach that all people are sinners. Genesis 9:6 shows that we are still essentially made in the image of God, although sin has certainly marred that image.
A clear Biblical example that God’s essential law is on everyone’s heart is seen in Genesis 4. Read the whole Bible up until that point (it won’t take you long!). God never commands people not to murder. Cain murders Abel and God holds him accountable and punishes him. The implication is that Cain knew better. God’s law was on his heart whether he would admit it or not. This is the same argument made in Romans 1:18-32. All people know there is a God, He has a moral standard for us to obey, we all sin and we all deserve judgement.
In Genesis 3:15, before God curses Adam and Eve, he makes a wonderful promise. He says that they will continue to live, have babies and that one day a child would come from their lineage and crush the head of Satan. This is the first prediction and promise of the Lord Jesus Christ. Where Adam had sinned, Christ would come, obey, and conquer.
Genesis 12:1-3 and 15:1-18 show God making a covenant with Abram (later called Abraham.) Genesis 15:6 makes clear that Abraham was saved by faith alone. This has always been and will always be how God saves people, through faith in God and the promised Child. See Galatians 3:6-9.
It seems that over time God’s grace to Abraham’s family (the Jewish people) began to go to their head. Many of them began to presume on God’s grace. God’s free grace should make us humble and grateful. Wrongly understood, it can make us arrogant and self-righteous. We can believe that we’ve done something to earn or deserve His grace. Matthew 3:7-9, Romans 2:28-29, Philippians 3:4-5 point to this error.
Partially because of this pride, God gave the Mosaic Law to humble people. Romans 3:20, 5:13-14, 20, 7:7-13, 2 Corinthians 3:7-9 and Galatians 3:19-22 show that the Mosaic Law was given to humble people and thus drives them to see how sinful they really were and how much they needed a Savior. The hope was that this crushing power of the law would drive them to beg Christ for mercy.
The Mosaic Law had three parts: the civil, the ceremonial and the moral. The civil was for Israel as a theocracy (a nation ruled directly by God.) It had to do with criminal law so to speak. Murderers were to be executed etc… It regulated how people were to interact with each other. It gave specific applications for that day and that culture on how to “love your neighbor as yourself.”
The ceremonial law had to do with the tabernacle and priests etc…. It had to do with being ritually clean and offering sacrifices for sin. It regulated how people were to interact with God. It gave specific applications for that day and culture on how to “love that Lord your God with all your heart, soul, mind and strength.”
The moral law was God’s eternal ethical law that had been on mankind’s heart since the beginning. It was summarized in the Ten Commandments. Three clear things made the Ten Commandments stand out from the rest of the Mosaic Law as central and most important:
1. Only the Ten Commandments were written directly by God’s hand.
2. Only the Ten Commandments were written in stone (implying permanence.)
3. Only the Ten Commandments were placed in the Ark of the Covenant.
Galatians 4:4-5 shows that Christ was born under this Mosaic Law for us. He fulfilled it for us. That is how we can be saved by grace alone, through faith alone, in Christ alone.
 Sinclair Ferguson, The Whole Christ, p. 150.