There are at least four lessons we learn from the Ten Commandments:
1. The Ten Commandments teach us that our relationship with God is of primary importance.
Hear, O Israel: The LORD our God, the LORD is one.  You shall love the LORD your God with all your heart and with all your soul and with all your might” (Deuteronomy 6:4-5)
And he said to him, “You shall love the Lord your God with all your heart and with all your soul and with all your mind.  This is the great and first commandment” (Matthew 22:37-38, emphasis mine).
God created us for Himself (Isaiah 43:7; 1 Corinthians 8:6).
2. The Ten Commandments teach us that our relationships with others are of secondary importance.
And a second is like it: You shall love your neighbor as yourself (Matthew 22:39, emphasis mine)
3. The Ten Commandments teach us that our relationship with God is conditional.
God standard is perfect righteousness.
And one called to another and said: “Holy, holy, holy is the LORD of hosts; the whole earth is full of his glory” (Isaiah 6:3)!
You who are of purer eyes than to see evil and cannot look at wrong (Habakkuk 1:13)
We’ve failed to meet that standard because even our best efforts are unrighteous.
We have all become like one who is unclean, and all our righteous deeds are like a polluted garment. We all fade like a leaf, and our iniquities, like the wind, take us away (Isaiah 64:6).
For all have sinned and fall short of the glory of God (Romans 3:23).
4. The Ten Commandments point us to Christ.
The Law exposes our sin.
What then shall we say? That the law is sin? By no means! Yet if it had not been for the law, I would not have known sin. For I would not have known what it is to covet if the law had not said, “You shall not covet” (Romans 7:7).
Consequently, the Law reveals our desperate need for something we do not have and cannot obtain by works: the righteousness God requires. This righteousness can only be received by faith in Christ.
So then, the law was our guardian until Christ came, in order that we might be justified by faith (Galatians 3:24).
“The law doesn’t help, it leaves us helpless; The law doesn’t justify us, it leaves us guilty; The law doesn’t grace us, it leaves us merciless.” These law/gospel distinctions are expressed in Christian song:
By God’s Word at last my sin I learned;
Then I trembled at the law I’d spurned,
Till my guilty soul imploring turned to Calvary
(William R. Newell, “At Calvary,” 1895)
The ancient law departs,
And all its terrors cease;
For Jesus makes with faithful hearts
A covenant of peace.
(Sebastien Besnault, “The Ancient Law Departs,” 1736)
The Law commands and makes us know
What duties to our God we owe;
But ’tis the Gospel must reveal
Where lies our strength to do His will.
The Law discovers guilt and sin
And shows how vile our hearts have been;
The Gospel only can express
Forgiving love and cleansing grace.
What curses doth the Law denounce
Against the man that fails but once!
But in the Gospel Christ appears,
Pard’ning the guilt of numerous years.
My soul, no more attempt to draw
Thy life and comfort from the Law.
Fly to the hope the Gospel gives;
The man that trusts the promise lives
Isaac Watts, “The Law Commands and Makes Us Know,” 1709,
In this sense, Ray Comfort is right. The absence of the Ten Commandments in our evangelism is “hell’s best kept secret.” Without the Ten Commandments, Jesus is not necessary to save us but merely to enhance our life. Why would one gladly receive a cure if one did not know that he has a life-threatning disease (cf. Matthew 9:12; Mark 2:17; Luke 5:31)?
The righteousness we lack and could never obtain on our own we obtain only by grace through faith in Christ alone.
For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God (2 Corinthians 5:21).
Four gloriously gospel-oriented lessons from the Ten Commandments.