Summary: There are significant positive results that make sex a sacred and profound endeavor, one that deserves special treatment. There are also negative consequences associated with sexual promiscuity.
Ephesians 5:3 But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God’s holy people.
Let's Talk About Sex
Sex is good. The Bible has taught this, literally, from the beginning. God's first commandment to humanity was "Be fruitful and multiply, and fill the earth" (Genesis 1 & 9). This commandment came long before any of the Thou Shalt Not's.
A few observations about that commandment:
1. God didn't say 'have sex & multiply", He said "Be fruitful & multiply". You can understand it as "have lots of sex and make lots of babies". But it seems like there is something more here, like fruitfulness is essential-God doesn't say do something, He says be something. Be fruitful. Sex is fundamental to our being. The fruitfulness sex enables is beautiful.
2. Sex has results. It is pleasurable (remember Sarah, when she was about 90 years old, said "shall I have pleasure, even when I am old?" when God promised her a son in her old age). But sex is not pleasure merely for pleasure's sake.
Sex has at least two results for which it was created. First, it is the means by which the two become one. One man, and one woman become one flesh (Genesis 2), one + one = one. Sex is the means by which God brings two people together in a form of intimacy that is both profound and fulfilling. This alleviates the first thing in creation that was not good. At the end of God's creative work in Genesis 1, God said over and over, "it is good", literally, very good. The first thing that was not good was that man was alone, without a mate. Sex enables two people to become one physically, emotionally, mentally and spiritually (this is one reason the Bible teaches it should be engaged in with such exclusivity). Thereby it alleviates the loneliness of our natural state. Sex is not the only means of intimacy in a relationship, but it is an important part of it. Maybe this is part of the reason the ancient Hebrew word for having sex was to "know" (Adam knew his wife Eve and she conceived, Genesis 4:1). The sharing of sex is so complete it knits two souls together. The second result is life.
I think we talk too little about how profound a privilege God has given us of bringing life into the world. Through sex, a physical act, a human, a spiritual being, is brought into existence. Without our cooperation that eternal being would not have a chance at life. When i was a child, most people thought of having children as one of their greatest goals. These days many people think of children as an inconvenience-a hinderance to accomplishing their goals. Families encourage young people to finish their education and build a career before having children, as if those things are first, or primary. If one is thinking of education and career as means to raise children in a more secure environment, there may be some validity to the argument. But i think most people are not necessarily reasoning in that way. Bringing eternal living beings into existence and raising them well is a far greater accomplishment than any degree or career, or fame, or individual achievement will ever be.