It is not clear how these claims are to be substantiated. One reason why someone might think that morality depends on God is that he or she accepts, explicitly or implicitly, the divine command theory of morality. This theory says that right or wrong, and good or bad, are given by the commands of God. The rules of morality, on this view, are simply the rules that God requires us to follow. So if there is no God to command us, there is no morality.
The objection runs as follows. Suppose we have an action X that is morally right. We can then ask, is it the case that X is right because God commands it, or is it the case that God commands X because X is right?
If it is the latter, then morality does not depend on God. So someone who subscribes to the divine command theory would probably say that the former explanation is the correct explanation of why X is right, that X is right because this is what God requires. The problem with this answer is that morality then becomes dependent on the arbitrary will of God. So if God says that we should torture innocent babies for fun, that becomes right and that is what we should do. If God says that we should be dishonest then again this is what we should do. But morality presumably is not this arbitrary.
Of course, someone might reply that God is good and morally perfect and so he would not command such a thing. But if morality does depend on God, there is no reason why God cannot issue such commands, since there are no additional moral constraints on what he should command. The only reason why God will does not require us to torture innocent babies is that there are independent reasons why those things are wrong, and God knows this. But then morality does not depend on God's commands after all.
If the meaning of life depends again on God's commands only, this would have the consequence that if God says that doing X constitutes a meaningful life, then this is what we should do. For example, perhaps God says that a meaningful life is to watch TV commercials for 24 hours a day for everyday of our life. Then this is how we should live our lives. But of course we would think it is absurd that a meaningful life can be achieved in such a manner. So again we have to conclude that what makes a life meaningful cannot be solely determined by God's commands.
U03.5 ExercisesSuppose someone were to reply to the argument in the Euthyphro problem as follows. "If God asks us to torture innocent babies or to watch TV commercials all day long, there must be some hidden purpose which perhaps we cannot understand. So even if God were to command these things, we should not infer that such commands are wrong." How should we respond to this argument?
Creativity takes courage.

Henri Matisse