The divine command theory is the ethical view that an action’s moral status is dependent on whether God commands or forbids it. A classic response to this theory is Euthyphro by Plato in which Socrates questions whether the gods make moral truth or merely recognize it.
Asking if the gods make moral truth is essentially questioning whether an action is moral due to their dictation no matter what. For example, we recognize killing an innocent as immoral, however if the gods said it was moral would that make it so? Most would say no.
On the other hand, if the gods merely recognize moral truth, this means that it must exist outside of their command and they have no control over morality, which is by definition an impious belief. These arguments against divine command theory were later used to counter Christian scholars on their moral theories.
However, there is another explanation that this rebuttal does not consider: the idea that man was created by God to be most benefited by God’s moral system. The argument hinges on the fact that without God these moral truths would still exist. However, this fails to recognize the fact that without God man himself would not exist, and should man not exist, then moral systems would not exist either.
As stated before, we can see that God’s moral system was created to apply to and benefit man. An example of this is the classic statement “thou shalt not kill.” If a man kills another man, he has committed an immoral act and gone against God’s teachings. However, should a star expand and engulf another star, eventually exploding, killing them both, the star is not immoral even though it is also God’s creation. This is due to the fact that stars were not created by God to abide by the same moral principles as man.
Another example is the black widow spider, which eats its mate after or sometimes even during mating. A devout Christian would not presume to call the black widow spider immoral for this action, although it is also one of God's creations. This is due to the fact that it, much like the star, was not made to follow the morality of man.
Moral concepts must be abided by man, therefore they must exist in congruence with man. Should man not exist, then morality could not exist either. Due to the fact that God created man, it then follows that God simultaneously created the moral systems which define him.
Some might counter this argument by claiming that man predates the very concept of religion. However, this argument assumes that God does not exist and was invented by man the same moment that religion was. This defense of the divine command theory is not an appeal to the existence of God or any other divine entity. It merely shows that if there is an issue with divine command theory, it must be proved by showing that God does not exist. However, it cannot be proven by simply claiming that if He didn’t exist, things would be a certain way. If there is a problem with divine command theory, it is a problem of faith and piety, or it is the inexistence of God.