Critics of the divine command theory say that if the theory is true, and god, therefore, lacks reasons for his commands, then

The decisions of God are arbitrary.

Explanation:

The Divine Command Theory also referred as Theological Voluntarism believes  that an action or a deed is morally correct if God commands it and is ethically wrong if God forbids it.

Thus based on the theory for an action to be morally right or wrong it depends on the command of God without proper rationale and depends entirely on what God commands.