Divine command theory

Divine command theory (or DCT, also known as theological voluntarism) — in the simplest of terms — states: An action or person is right/wrong/good/bad if and only if God said so.

A slightly more formal definition states:

An action's status as morally good is equivalent to whether it is commanded by God.

All you need to know regarding why this is true: because God said so.

DCT shares its underlying assumptions with the argument from morality, though it doesn't stop there.

In effect, DCT makes morality a dictatorship, as that and only that which the Supreme Leader wants is good, and literally everything he didn't ask for — or happens to retrospectively condone on a whim — is bad. Free will becomes nothing but the power to do evil by this definition, as even trying your best to only follow every literal word of God will prove impossible. On the plus side, DCT solves the problem of evil, as whatever God wanted was good, and whatever he didn't want wasn't good. Off the hook, scot free!

Any form of non-religious morality is obviously made categorically impossible in this view. The upside is that, from this viewpoint, quoting scripture at people like an asshat is considered ethical! Hooray!

Despite the name "divine command theory" containing the word "theory", adherents reliably fail to apply their favorite fallacious criticism against it.

Formulations, allegedly
According to the Bible, in reference to the tree of the knowledge of good and evil, God had told Adam and Eve:

Since God created such a tree, every piece of knowledge of Good and evil comes directly from God.

Various verses have attributed God as sovereign, or judge and ruler of all. If anything is good for the reason other than his commands then He is not in charge of everything.

As a code word
DCT theory is the code word for "I'm defining morality that uses God to label disagreement/dissent as evil/immoral."

The argument is that since God communicates in revelations, it is indistinguishable between an actual revelation to the speaker and stuff made up by the speaker. Since the revelation is attributed to God, anyone disagreeing with the speaker can be labeled as disagreeing with God.

Scriptural morality, in a similar manner, is the code word for "I said the book is right, so I am quoting it in the way I like in order to convince people that the morality I made up is correct."

These can be used to label debate opponents negatively in a debate, especially a debate about morality.

Euthyphro dilemma
In a nutshell: does God say it is good because it is intrinsically good, or is it good because God says so?

Authenticity of revelations
The underlying assumption is that God communicates through revelations, which, the assumptions made in the definition of God (specifically, existence of omnipotent beings) will make it difficult to validate the authenticity of revelations without using special pleading (That God's existence is unique in set of omnipotent beings, and God is omnibenevolent). See the derivation here.

Uniqueness of summum bonum
If it is good because God says so, then there exists a unique Summum bonum (the highest good), namely, approval by God. The existence of a unique highest good means one should sacrifice everything for it and derive everything from it, including but not limited to: and the exchange should be taken at every opportunity regardless whether God approves any and all of those things, because (i) God approving those things by no means imply the individual possessing such things will be automatically approved/commented and (ii) the assumption is that God is capable of changing opinions from time to time.
 * Consciousness (including consciousness to being approved by God)
 * Knowledge (Including knowledge of what will get God's approval, and knowledge of whether God actually exists)
 * Wisdom (Including the biblical definition of "Fear of God")
 * Free will (Refutes theodicy)

On the contrary, if "being conscious that oneself is being approved by God" is the summum bonum, then such consciousness may be merely an illusion due to the authenticity of revelation problem.

Interpretations of scriptures
If the source of ethical propositions come from the scriptures, an additional issue arises that concerns with how to interpret the scriptures correctly. Christianity, for example, can have various interpretations on the same issue. Take killing people for example:
 * Story of Cain and Abel: Killing carries additional punishment on top of the one from the original sin.
 * The Ten Commandments is translated as saying either "Thou shalt not kill." or "Thou shalt not murder." But God actually commands killing, even genocide, elsewhere, and if the commandment is merely against "murder", then it requires a pre-existing legal code establishing just what "murder" is (and since "murder" is "killing that is not allowed", saying "murder is not allowed" is rather tautological).
 * God killing people, for some reason, is justified, every single time (by calling God "good" and "just").
 * Satan killing people, for some reason, does not come with corresponding punishments (perhaps due to being contracted out from God).
 * It is assumed that justified killings are performed for every instance of capital punishment for this list of crimes in the Old testament, which is rather convenient considering that appeal processes do not exist back then. Not that you will need the appeal process if you just send everyone to the afterlife and let the almighty sort them out given his omniscience.  With his omnipotence He should be able to put you back to life in one way or another in case you are wrongfully convicted.
 * Biblical battles mandates that any non-virgin women and men in the settlements besieged by the Israelites are to be killed after a successful siege regardless whether they have participated in the battle.