The Ten Commandments were given to the Israelites so they could know how to honor God and live in a thriving society. The first four commandments mostly dealt with the vertical relationship with God and the last six primary deal with the horizontal, one another, relationships.
"You shall not commit adultery." Exodus 20:14
This command is sandwiched betwixt not murdering and not stealing, and therefore should be met with as much weight in our minds as those two commandments. Yahweh is serious about His people not committing adultery.
What is adultery? Adultery, by definition, is voluntary sexual interactions between two people that are not married to one another when at least one of the parties is married to another. The Bible has much to say about fornication (any sex outside of the bounds of marriage) but we will stick to simply adultery in this post.
Fidelity is something we have attempted to avoid for generations and have not learned a single lesson about. In the Old Testament we read stories of polygamous men. Some may say that the Bible condones polygamy, but it doesn't. In every story about a polygamous family we see friction and in-fighting amongst the husband and his wives, the wives amongst themselves and even murder amongst the children. Polygamy didn't and doesn't work. Now the term is of choice is polyamory, meaning multiple sexual relationships at once though not necessarily amongst married people. Books like The Ethical Slut have popularized this. I have had a youth at church talk about how his girlfriend claimed she was polyamorous (I said that's a fancy word for cheater). I read that Willow Smith, the 20 year old daughter of Will and Jada Pinkett Smith, recently came out as polyamorous. She claimed this consensual non-monogamy was a way to prevent the sting and lying that comes from infidelity in monogamy. My point is, there is nothing new under the sun and the same old garbage won't work even under a fun, new name.
God calls those who wish to enter a sexual relationship into a committed, one man with one woman, marriage until death parts the spouses.
I believe one of the main reasons God does this is because healthy, committed marriages are good for society. They are the bedrock of good families which are the bedrock of good communities.
So, how do we not break this commandment. If our urges since the entrance of sin into the world seemingly compel us to all desire to cheat, how are we to keep the 7th Commandment? I won't offer an exhaustive list, but I will give a few ways.
1) Take Every Thought Captive
The battles won by the body are usually first won by the mind. Take your thoughts captive (2 Corinthians 10:5) and put them under the Word of God and the guidance of the Holy Spirit. No person commits consensual adultery without deciding first in their mind to do the deed. You may say one could have sex with a married person without knowing, but obviously even that person would have first decided to not put themselves under the Word of God.
"You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. If your right eye causes you to sin, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into Hell. And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into Hell." Matthew 5:27-30
Jesus turned the heat up on this commandment. He tells us that sin germinates in the mind, even if the sin plant blooms elsewhere.
This battle is hard. I will not lie to you; I lose this battle sometimes, but I/we must fight it. We must fight it with a total war. We don't flirt with this kind of sin, we either cut things out that tempt us to sin or we lose.
2) Spend Our Sexual Energy on Our Spouse
At the risk of making my in-laws blush, I say spending my sexual energy on my spouse is a wonderful infidelity protection. I lack no good thing sexually in my marriage despite what Satan may try to say. Sexual energy doesn't all have to be "sex" but anything you would feel guilty doing and thinking with and about another can be spent instead on your spouse.
God created our urges in this department. The demon Screwtape (The Screwtape Letters) said to his evil nephew that: "Never forget that when we are dealing with any pleasure in its healthy and normal and satisfying form, we are, in a sense, on the Enemy's (God's) ground... He (God) made pleasure: all our research so far has not enabled us to produce one. All we can do is encourage the humans to take pleasures which our Enemy (God) has produced, at times, or in ways, or in degrees, which He (God) has forbidden."
Here's good news: God made sex to be experienced and enjoyed between husband and wife. Satan lies and tells us that this pleasure is best experienced in many ways other than the best, but God made it and knows best. Therefore, enjoy His good gift as much as you and your spouse can agree to enjoy it together.
3) Hold On & Trust God
But what if it's not easy? What if my wife's sexual needs and mine don't come close to aligning? What if my marriage is in a hard place and my opposite sex friend seems like a refuge? What if the world says fidelity is for losers? What if there is no outlet for my sexuality? What if my marriage feels like it's crumbling? What if I don't find any joy in keeping this commandment?
Hold on and trust God.
There is no commandment in Scripture that isn't for God's glory and our good. Even when we can't see it from our perspective we have to trust that God knows the best ways to use His gifts. Even when culture tries to neuter sin and make it seem tame. Even when celebrities and "experts" apply copious lipstick on the pig, it's still a pig. Even when the good gift is advertised as lame and lacking, we have to trust that Father knows best. There will be reward for keeping the 7th Commandment.
"Marriage should be honored by all, and the marriage bed kept pure, for God will judge the adulterer and all the sexually immoral." Hebrews 13:4
Honor God and honor your marriage and every marriage and keep the marriage bed pure today.