1. Because God decreed it so. God made a simple commandment that anyone can understand and follow: "Thou Shalt not commit adultery". He doesn't make commandments that are impossible to follow or that are intended to make us unhappy.
2. Unchastity is next to murder in severity. Think about it, how are STD's spread and how do the victims die? Then there is the rare tendency for the break up of a sexual relationship to result in suicide. Not to be ignored, of course, is the glaring dilemma of an unwanted pregnancy. How many children are destroyed before birth? Is the destruction of human life not murder? Murder is so heinous because human life is of inestimable value. Is an unborn child of no value? Tell that to the myriad of infertile married couples pining for children of their own.
3. Girls need to know, boys always tell, and sex doesn't mean the same thing to boys as it does to girls. How will a girl feel when she gives sex to a guy and it becomes the dirty joke the football team is laughing about? How will she feel when she sees that same guy she had sex with kissing another girl? Sex outside of marriage is a recipe for misery.
|image lifted from Picky Wallpapers|
One more note: Somehow, and for some reason, our society is completely obsessed with sex. Sex is important, in fact, it is so important that the drive to sex is only superseded by the instinct to survive; however, it's not something we should obsess over. No happy person obsesses over their next meal, or whether a murderer is lurking around the corner; so why are justified in such a fixation on sex and sexuality? The sum of one's character is not measured by how much of what kind of sex that individual is or is not getting. It makes no sense, so stop obsessing.
By no means is this information on sex comprehensive I'm sure as parents we can find many other healthy things to tell our children about sex, but we need to start being honest with our children about sex.