There is no legitimate moral claim without an acknowledgment of God. Here is a proof.
Do you believe that there is any act which is wrong? Wrong or evil without any doubt? Objectively wrong?
If no, then you can never, ever object to any act no matter how heinous, inhumane, or cruel. For all our sakes, I hope you didn’t say no.
If your answer is yes, you have confirmed the objective existence of a moral law, a full code of right and wrong, good and evil.
A moral law requires that there is a moral law-giver.
Yes, it does. Here’s why:
The moral law at no point seems as though it evolved from a random or amoral process.
When we examine the moral law at any point, we find that it has certain characteristics and lacks others. It is purposeful or systematic, not random. It pushes us toward self sacrifice and interest in others well-being. Morally, it compels us to choose the more selfless and less safe options.
It derives from a mind rather than from a mindless process.
The mind it derives from has clear preferences. It loves love and hates hate. It strongly prefers that we behave toward other human beings with things like kindness, love, mercy, and justice.
How do I justify that claim?
Let’s go back to your agreement that there are some things that are just wrong. When we look inside ourselves for that sense of right and wrong, we find that there are innate, intrinsic convictions. Those convictions tell us to be kind, not cruel. To be fair, not unjust. To respect other people, not victimize or dismiss them.
It’s not that we succeed in behaving according to those convictions, but that we all know they are there, that they do not change, and that we ought to obey them.
So where are we? We believe that there is an objective moral code. We find it inside ourselves and we hold everyone else accountable to it as well. We see that the moral code necessarily has a source which is a mind with sentience and preferences.
That code of preferences about our behavior, or its source, seems even to hold some authority over our moral choices.
We are now talking about a personal being with a mind and perfect, consistent moral goodness.