Our Sexual Design: Heidelberg Catechism Lord’s Day 41


  1. What does the seventh commandment teach us?

That all unchastity is accursed of God,1and that we should therefore loathe it with our whole heart,2 and live chastely and modestly,3 whether in holy wedlock or single life.4

[1] Lev. 18:27–28. [2] Jude 1:22–23. [3] 1 Thess. 4:3–5. [4] Heb. 13:4; 1 Cor. 7:1–4.


  1. Does God forbid nothing more in this commandment than adultery and such gross sins?

Since both our body and soul are temples of the Holy Spirit, it is His will that we keep both pure and holy; therefore, He forbids all unchaste actions, gestures, words,1 thoughts, desires,2 and whatever may entice thereto.3

[1] Eph. 5:3–4; 1 Cor. 6:18–20. [2] Matt. 5:27–30. [3] Eph. 5:18–19; 1 Cor. 15:33.

Our Sexual Design 


Marriage is a gift from God and was seen from the beginning as the normal state of humanity.  It was not good that the man should be alone, God said, and it was that need for companionship and intimacy which was the original impetus for marriage.  Note that it was not childrearing, though that was an important function of marriage as well.  The witness of Scripture throughout, including the Seventh Commandment, is that man’s sexual nature is designed to function exclusively within the confines of marriage.

When evaluating the Old Testament civil laws regarding marriage, adultery, fornication and the like, it is important to remember Jesus’ words regarding divorce, in Matthew 19, that Moses permitted them to divorce because of the hardness of their hearts.  This is an important insight into the nature of Mosaic civil law.  It was not intended to express God’s perfect moral will, but rather was intended to regulate and restrain the sinfulness of the people, in order to limit the damage that such sinfulness inflicted, especially on the poorest and weakest in society.  So a man who wanted to put his wife away had to give her a writ of divorce, so that she could prove that she was free to remarry.  This did not indicate that God thought divorce was a good idea.  As Jesus said, the intention from the beginning was the unbreakable union of a man and a woman together in matrimony.

Sexual Immorality and Its Consequences

It is in this context that the many commandments against sexual immorality must be understood.  Our sexual natures are a great gift from God and a great aid in promoting and enjoying the union of man and woman in marriage.  It is precisely because sexuality is such a powerful aspect of our being that it must be carefully regulated.  Fire is a wonderful blessing and civilization would be impossible without it.  But fire must be contained properly or it causes enormous damage.  So too, an unrestrained sexuality is a deadly force.

Sexual activity with another person causes the development of feelings of very close intimacy with the other person.  It does this because this is what it is designed to do.  This is true of any level at all of sexual expression, however innocent seeming, which is why Jesus says that even looking with lust causes the commission of adultery.  When that intimate relationship begins to be formed and then is broken, emotional damage results.  It becomes increasingly difficult to form normal emotional relationships.   This is just one example of the damage done by adultery, but we lead with it because all too often as society thinks it has gotten better at mitigating the external damage of unrestrained sexual expression, it has completely neglected to recognize this spiritual and emotional aspect of our natures.

Beyond that, of course, sexual immorality causes a great deal of damage in other ways.  Physically it spreads terrible disease.  Societally it breaks down the bonds that holds human civilization in place, as it undermines marriages and results in children being born and raised in unsafe and unstable environments.  Materially it is tremendously expensive for the whole community– having a child born out of wedlock is one of the surest routes to poverty, and being raised in a single-parent home is a high predictor of a great many social ills such as illiteracy, substance abuse, and criminal behavior.  Pornography may seem like a harmless sin, but in addition to the many women and children who are forced into this industry against their will, the spiritual and emotional damage is real and substantial.

We think that through government programs, medical treatment and educational initiatives we can control the damage that is caused, but the actual result is that people, especially the young, are lured into complacency and a false sense of security and become even more unrestrained in their behavior.  Contraceptives only work when used carefully and responsibly, and even then only partially.  Little can help the spread of destructive venereal diseases, though medication can reduce the damage somewhat.  Abortion can solve the problem of out-of-wedlock or otherwise inconvenient pregnancies, but only at the expense of much greater physical and spiritual problems.

More could be said about specifics (such as homosexuality, cohabitation, and divorce), but all of this is to say that God designed human nature to work in a particular way both physically and relationally, and when we flout God’s design for humanity, the result is predictable.  As certainly as putting orange juice in our gas tank will ruin our engine, defying God’s design for our sexual natures will result in all sorts of damaging consequences.

The Gospel and Sexual Sin

As with all of God’s commands, however, we operate under God’s grace.  Even for those with great sins in their past and present, the blood of Christ is sufficient, and the grace of God is powerful to heal and restore.  Sexual sins are very prominent, and sometimes get singled out particularly by conservative churches as especially worthy of condemnation while slander, gossip, greed and the like go on largely unremarked upon.  On the other hand, the prominence of sexual sin in our culture has driven all too many churches to compromise and be silent on this issue.  We ought to avoid both of these extremes, and instead exhibit the grace of God to others, witness to the goodness of God’s law and the promise of forgiveness and healing in the gospel of Christ.