There are three doctrines, which are held (generally) by Christianity, of which the first two are also shared with the other great Monotheistic faiths, Judaism and Islam.
1) God is good. 2) God wills us to do what is good. 3) God is the basis of ethics.

Le Poidevin points out that the first two are not implicit to the idea of a creator, however, the third premise can be used as the basis of the moral argument for the existence of God.

Plato, in his Euthyphro, identified a problem with the acceptance of all three premises; the third doctrine, namely that God is the basis of ethics, makes it difficult for us to understand the other two doctrines. He presents us with the question, “How are we to understand the idea that God wills us to do what is good?”. To which there are two possible answers, either (a) God wills us to do what is good because certain acts are of themselves good, and he wishes them to be performed, or (b) An act is good only because God wills it. As Le Poidevin states, neither of these answers are wholly satisfactory to the theist, for they both raise problems with theistic belief, as we understand it.

If we accept the first answer, that certain acts are good independent of God, and it is their natural goodness that makes God will them, then it follows that moral values are independent of God. Therefore if God did not exist, there would still be moral values, thus the moral argument for the existence of God is scuppered, and the basis for ethics has nothing to do with theism.

If on the other hand we accept the second answer, that an act is good solely by the virtue of God’s willing it, then we are confronted with another problem; namely that “God wills us to do what he wills us to do”. Therefore, returning to the three original doctrines that we considered, it would seem that God’s willing us to do what is good, is contrary, under a metaphysical interpretation, to the concept that God is the basis of ethics. There is also a contradiction between the notion of God being good and being the basis of ethics, for “if ascribing goodness to something just means that God wills it, then the assertion that God is good becomes the curious and morally empty assertion that God wills that he be as he is”

This renders the arguments that God is the basis of ethics, and that morality is a demonstration of God’s existence, as logically incoherent and therefore false. This is the meta-ethical argument for theism, which takes the following formula:
1/ If theism is true then ‘God is good’ is morally significant.

2/ If theism is true then God plays an explanatory role in ethics.

3/ If ‘God is good’ is morally significant, then moral goodness must be Independent of God.

4/ If God plays an explanatory role in ethics, moral goodness cannot be Independent of God.

Therefore the conclusion that theism is false is reached the following way, 1 and 3 considered together, imply 5:

5/ If theism is true then moral goodness must be independent of god.

But also 2 and 4 mutually considered imply 6:

6/ If theism is true then moral goodness cannot be independent of God.

Positions 5 and 6 therefore provide us with the conclusion that, If theism is true then moral goodness both is, and is not, independent of God. A self-contradictory and seemingly false position.

But the Christian or theist response can be found if the third proposition is re-considered, for it is necessary to explore the meaning of the term ‘goodness’. If we look at Plato’s question (“Does God will us to do what is good because, independently of him, it is good, or is it that what is good is so only because he wills it?”) we find that it is assumed that we must choose one premise or the other and not both. Although at first it would appear that we couldn’t accept both positions. If we attempt to define ‘good’ in more than one way, then it is possible that ‘good’ acts can be independent of God’s will, but also that in another sense of the term, ‘good’ acts are good because he wills them. If the theist position can justify this argument, then it is possible that they can escape the meta-ethical argument.

What is needed is to distinguish between two elements in morality, descriptivity and prescriptivity.

Descriptive morality identifies acts that when done, would bring about a particular beneficial consequence. But there can also be an ‘ought’ statement in descriptive morality, which is of its nature conditional, so for example ‘one ought to eat, if one wants to stay alive’. (The ‘ought’ here is Hypothetical). Prescriptive morality, on the other hand, suggests an obligation in our actions, ie. If we wish to achieve x we ‘Must’ do y. Or to put it another way, a prescriptive sense of ‘good’ carries an unconditional ‘ought’: for example, “one ought to stop killing, full stop, and not merely to avoid censure”. In making this distinction and asserting that there are acts, which are prescriptively and unconditionally good, as well as the conditional descriptive acts, we are “assenting to a certain conception of morality”.

So the theistic response to the meta-ethical argument is to say that something can be descriptively good, which is in our best interests and which is independent of God’s will. And at the same time we can say without contradiction that there are those things that are good because God wills it.

The final consideration that the theist needs to make is the concept that ‘God is good’. The meta-ethical argument suggests that either ‘God is good’ is morally insignificant, or moral goodness is independent of God. The approach to this dilemma that Le Poidevin adopts is that when we say ‘God is good’ what we are doing is applying an analogy of God’s goodness to a morally good member of the human race. For example morally good parents would take care of their children, in the same way that God can be said to take care of his creation. But also implied in the statement ‘God is good’ is that unlike humans, God is a source of moral value, his goodness consists of the fact that he is the origin of ethics. If he were the basis of ethics, then we would agree that such a role would not be insignificant, and comparatively, as Le Poidevin suggests, neither is the concept of ‘God is good’.

Therefore the theist can amend the third premise in the meta-ethical argument; so instead of reading:

If ‘God is good’ is morally significant, then moral goodness must be independent of God.

It should instead read:

If ‘God is good’ is morally significant then moral goodness is not independent of God.

This line of argument has often been used as a defence against the implication from Darwin that humans as a species are not unique or that we are created moral beings.