All the commandments reflect the nature of God, but perhaps none do it as completely as the seventh.  God is completely faithful; He is a God of covenants and He is three persons united as One in perfect intimacy and shared submission.  He created man in His own image and thus created him to need intimacy with others.  The command to be faithful within marriage goes to the heart of who God is and how He created.

Marriage
The basis for this command really goes back to the beginning of the world.  The creation account tells us that God created man in His own image, in the image of God He created him; male and female He created them (Gen 1:27).  The relationship of Adam and Eve was to model the Trinity; they were male and female in the image of God.  When Adam first saw Eve he said, “This is now bone of my bones, and flesh of my flesh; she shall be called woman, because she was taken out of man.”  And Moses comments that for this cause a man shall leave his father and his mother, and shall cleave to his wife; and they shall become one flesh (Gen 2:23-24).  The cause Moses refers to is to reunite into one flesh – to be two in one.  Marriage reflects God’s intent at creation to make man in His own trinitarian image.

The command also reflects God’s concern for covenants.  God is a covenant-making and covenant-keeping God.  When Adam and Eve sinned in the garden He promised to send a Messiah to redeem the world (Gen 3:15).  After the flood He made a covenant with Noah that He would never again destroy the world with water and used a rainbow to signify it (Gen 9:8-17).  He made covenants with Abraham and Moses to establish a nation through which the Messiah would come and preserve that nation in the Promised Land.  All covenants were fulfilled because God cannot violate His word.

In the same way, He takes very seriously the covenants His people make.  God sent a famine on Israel during David’s reign because the nation violated a several-hundred-year-old covenant with the Gibeonites made during the time of Joshua (II Sam 21).  The covenant was old and forgotten and made with a people who deceived Israel to attain it (Josh 9) and yet God still punished the Israelites for three years until they made it right.  God is a covenant-keeper and expects His people to be the same.  There is no such thing as a meaningless covenant in God’s eyes.

In that light it is easy to understand the importance God places on a marriage covenant.  When two people promise to be faithful to each other until death, God expects them to honor their word.  Adultery at its core is the breaking of a covenant, and God views covenant-breakers very harshly.  When you make a vow to the Lord your God, you shall not delay to pay it, for it would be sin in you, and the Lord your God will surely require it of you (Deut 23:21). 

Another element of marriage that highlights the gravity of this command is how it models God’s relationship with His people.  The Bible uses the marriage metaphor repeatedly to illustrate that God’s people are joined with Him in covenant relationship.  In the Old Testament God oftentimes refers to Israel’s idolatry as spiritual adultery (Ezekiel 16:32).  In the New Testament the church is pictured as Christ’s bride (Eph 5:22-25) and James says to love the world is to be an adulteress (James 4:4).  Thus marriage is not only a picture of the Trinity, it is a picture of the unity the believer has with his Savior.

The Ephesians 5 passage really elaborates on this point.  Paul says the husband is the head of the wife as Christ also is the head of the church.  The husband should give himself to his wife and love her as Christ loved the church and gave Himself up for her.  The husband must cherish his wife as Christ cherishes the church.  As members of Christ’s church we are members of His body – we are actually in union with Him in the same way a husband and wife are one flesh (see also I Cor 6:17 and Rom 7:1-6).  Marriage is sacred because of what it pictures – it reflects the union we have with Christ now and previews the perfect union we will have with Him in the next life.

Its basis in creation, its status as a covenant and its role in picturing the union we have in Christ all underscore the importance and gravity of marriage.  There is a reason adultery is listed next to murder in severity.  To be unfaithful in marriage is to dishonor the most fundamental human relationship and wreck what best demonstrates our created purpose as image-bearers.

Sexual Sin
There is more to this command, however.  Jesus discusses the seventh commandment in the Sermon on the Mount.  In Matthew 5:27-28 He says, “You have heard that it was said, ‘You shall not commit adultery’; but I say to you, that everyone who looks on a woman to lust for her has committed adultery with her already in his heart.”  He explains here as He did with the sixth commandment’s prohibition of murder that it is the heart that counts.  It is not simply the physical act of adultery that violates the command – it is the thought that leads to it.  The Ten Commandments are not concerned only with actions – they make claims on our thoughts and motives too.

With this in mind it becomes clear that the seventh commandment really is a command against sexual sin of any kind.  All sexual sin includes lust, so if lust is the real issue than all sexual sin is addressed.  The man dabbling with pornography is guilty.  The one who fantasizes about another is guilty.  The one who simply likes to ogle men or women is guilty.  The standard – as it is with the sixth – is impossibly high (and cries out for the gospel).

That it specifically addresses sexual sin raises the stakes of this command.  Paul says in I Corinthians 6 that sexual sin has a component that makes it different from other sin.  He says in verse 18, “Flee immorality.  Every other sin that a man commits is outside the body, but the immoral man sins against his own body.”  If the one flesh relationship within marriage has a spiritual component in how it models the Trinity and our union with Christ, then a sexual relationship outside of marriage is a unique violation of God’s intimate relationship with His children.

This points to how powerful sex is.  If sex is meant to be a key component in the one flesh relationship (note that it is not the only component – becoming one flesh involves more than physical union – it includes intimacy and commitment and vulnerability at every level) and is meant to maintain unity for a lifetime, then it obviously is very strong.  And like anything that is extremely powerful it can wreak havoc and cause enormous damage when it is used irresponsibly or used for something other than its intended purpose.  Sexual sin is so dangerous because it takes one of the strongest drives God created and points it at ourselves.  What was intended to be glorious when focused on someone else becomes deadly when focused on self.

Proverbs 5
One of the best passages to address the seventh commandment is Proverbs 5.  In this chapter Solomon counsels his son on the dangers of adultery and the wonders of marriage.  He both warns and encourages and in so doing gives a roadmap for what to fight and how to fight it.  We do not merely avoid sexual sin; we must also celebrate sex as God intended it.

Solomon warns his son that an adulteress promises short-term pleasure at the expense of long-term pain and must be avoided at all costs (it IS interesting that a man with 700 wives and 300 concubines advises his son on the gloriousness of monogamy – this seems to be a classic case of, “Do what I say, not what I do”).  Her lips drip honey but in the end she is bitter as wormwood.  Keep your way far from her, and do not go near the door of her house.  This points to the strength of sexual temptation.  For some sins we are to resist the devil and watch him flee (Jas 4:7) but for others we are to let the devil watch us flee.  Do not go where sexual temptation is likely to exist – do not put yourself in the way of it.

Solomon goes on to warn his son about the ramifications of adultery (and really all sexual sin).  You will give your vigor to others, and your years to the cruel one (waste the prime of life).  You will groan at your latter end, when your flesh and your body are consumed; and you say, “How I have hated instruction!  And my heart spurned reproof!”  Sexual sin ALWAYS ends in deep regret and pain.  “You do not break the seventh commandment; the seventh commandment breaks you.”

Solomon thankfully does not limit his advice to a warning.  He continues and gives us the positive side of the seventh commandment along with a strategy to fight sexual sin.  He says to drink water from your own cistern, and fresh water from your own well.  Should your springs be disbursed abroad, streams of water in the streets?  Do not waste your sexual energy outside of marriage – keep your sexual relationship to your wife only.  Let your fountain be blessed, and rejoice in the wife of your youth.  As a loving hind and a graceful doe, let her breasts satisfy you at all times; be exhilarated always with her love.  Note that he phrases these statements as commands – he does not mean this to be optional.  Sex within marriage is wonderful!  Rejoice in it!  Revel in it!  Do not mess up what you should exhilarate in!  [Notice how frank and erotic Solomon is here?  It is interesting that oftentimes the Bible is much more straightforward and blunt than we in western Christian culture are.   OT Hebrews were not nearly as uptight as we sometimes are about any and all physical acts.]

He ends with a sober warning.  He says that the ways of a man are before the eyes of the Lord, and He watches all his paths [Tim Keller makes the point in a sermon on this text that the word for paths refers to wagon tracks.  A wagon makes tracks by going over the same ground again and again, but once the tracks are made the wagon has no choice but to follow them because they are ruts that do not allow for any other route.  The same is true of sexual sin.  When we continually play with it we eventually lose the ability to avoid it).  God does not miss anything we do – we know this – but He certainly does not miss when we violate something as sacred as a marriage covenant.  Sexual sin is serious and God does not leave it unpunished (I Thess 4:1-8, Matt 5:29-30, Job 31:1-12).  His own iniquities will capture the wicked, and he will be held with the cords of his sin.  Sexual sin controls the sinner – never the other way around.  The one who engages in sexual sin ultimately becomes enslaved.  He becomes like Ahab who sold himself to do evil (I Kings 21:25).  It is as if he jumps up on the platform at a slave market and says to sin, “Buy me!  Buy me!”

Perhaps the best way to end our look at Proverbs 5 is to focus on the most encouraging part of Solomon’s advice.  In verse 20 he says, “For why should you, my son, be exhilarated with an adulteress, and embrace the bosom of a foreigner?”  If true sexual fulfillment – the kind God intended for His creatures from the time He created Eve as a companion for Adam – is to be had outside of marriage, could Solomon say this?  If we are – as many in our current culture say we are – merely animals that were never meant to enter into monogamous relationships for life, would Solomon ask this question?  The reason Solomon can say this is because pursuing sexual satisfaction outside of a lifelong marriage is not only immoral and ungodly – it is foolish!  We do not just court disaster when we look for immoral sexual satisfaction, we settle for what is inferior!  Sexual intimacy between two people who have vowed to become and stay one flesh for life and who have the glory of their Creator as their mutual goal is a wonderful gift of God that cannot be replicated in any other relationship.  [Is it not a mark of how sin has perverted God’s gift of sex that the world says sex within marriage is boring but sex with multiple partners is exciting? And yet the Bible teaches that this is the exact opposite of what is true!  We were MADE to find sexual satisfaction within the confines of a one flesh relationship.  There is no ‘morning after’ or ‘walk of shame’ for believing spouses.]

Sex is glorious not only because it reflects the joy of the Trinity but also because it points to the eternal delight of soul that we will have in heaven, in our loving relationships with God and one another.  Romans 7:1ff tells us that the best marriages are pointers to the deep, infinitely fulfilling, and final union we will have with Christ in love.  – Tim Keller, The Meaning of Marriage

Fighting
We fight against sexual temptation in the same way we fight other sins but with a couple of additions that owe to its strength and distinctiveness.  To fight any sin we must first focus on our relationship with God through the gospel (which we preach to ourselves continually).  We keep before us that we are fully justified and can live in His presence glorying in His love and acceptance. We will never – because of our fallen nature – avoid sin merely by reminding ourselves of its consequences.  We must first revel in what we have in Christ and make sin less attractive by comparison.

If we are married we must fight temptation by celebrating our sexual relationship with our spouse.  A married couple who rarely has sex (and sins by the omission – I Cor 7:1-6) opens itself up to all kinds of sexual temptation.  The celebration of sex within marriage acts as a deterrent to sex outside of it.

Finally we must walk by the Spirit (Gal 5:16-25).  It is only in the power of the Spirit that we can fight against something as strong as sexual temptation.  To face continual temptation (and it truly is continual in a culture where technology makes it available easily and at all times – the level of temptation we now face is unparalleled in Christian history) alone is naïve at best and life-destroying at worst.  Even setting up boundaries and safeguards – which is good to do – ultimately will not work without the Spirit’s help (there is ALWAYS a way around the boundaries).  We MUST walk in the strength of the Spirit if we are to have victory over sexual sin.  We must live a life of quiet desperation that acknowledges our weakness apart from the Spirit’s help.

On a more practical level:

• Memorize scripture to fight against the mental aspect of sexual sin.  We cannot simply remove temptation or sin; we must replace it with something else.  Nature hates a vacuum and so does our mind.  If we do not want to have lustful thoughts we must fill our minds with something to crowd them out.
• Live counter culturally if need be to avoid temptation (give up the media or the technology).  If Christ said we should cut off our right hand our gouge out our right eye to remain pure, it makes sense that we should be willing to do whatever it takes.
• Expose sexual temptation to the light – tell others about specific struggles.  The Enemy loves it when we keep sins in the dark.  Sexual temptation is uniquely secretive because sex as a whole tends to be considered what we do in secret.  Exposing temptation and sin does much to blunt their power and allure.
• NEVER take an arrogant approach to sexual temptation.  The Enemy loves it when we think we can handle things others cannot.  Everyone is fallible and all of us are susceptible to the worst sins.  Sex is too powerful to toy with.  The wise man does not take matches and gasoline and assume he knows better than others how to handle them without getting hurt.