Atheists think it's all so simple. It's actually so complex, it defies human imagination. It is only their tiny brains that are simple.
In the injunction against fornication, the Almighty is trying to protect you against things you cannot possibly even comprehend, forces working against you which have a peculiar brilliance of their own which is difficult to even describe.
Our ancestors called them demons because that was all they could grasp.
There is a rich microcosm and macrocosm around you that regards you with such indifference it cannot even be described as despising you, rather it is capable of annihilating you by means of your own actions without you even knowing what you are doing to yourself.
Basically, if you adhere to the ten commandments and fear God, things will tend to go well for you if it is accompanied by your repentance to Christ. Maybe you just aren't smart to understand how and never will be. Nonetheless, if you let God be true and every man a liar, things will be well with you in some way that is very hard to articulate. On the other hand, if you do not fear God and proceed on your own wisdom, things will not go well for you. I can assure you of this. I was an atheist for sixteen years and there's a reason nothing was ever quite right for me. When you walk away from the protection of God, you are entering a very dark universe with some very nasty entities working on many different levels of reality all at the same time ... the one thing they have in common is that they will all expedite your destruction. You can always tell when atheist ideas are infiltrating a population. It's when they begin to die.