1) I’m not actually a divine command theist, and I don’t think my conclusions necessarily lead to that point. The moral law comes from God’s nature, but there still need to be consequences for breaking it. That doesn’t make it arbitrary.
2) This is important, so pay attention: When I say the moral law needs to have consequences for it to be a moral law, I am not saying that the only reason to obey the moral law is fear of consequences.
What do I mean by this?
Let’s say I am building a house for my family and me. A crazed philosopher comes up to me and says, “Why do you need a house anyway?”
Confused, I answer “Because without a house my whole family will be stuck sleeping in the cold, outside, which can be potentially dangerous. We need some sort of shelter.”
And so the philosopher smugly replies, “So you are saying that the only reason to build a house is because it provides shelter! Are you sure you want to make that claim?”
Except, no, that’s not what I’m saying. There are all sorts of reasons to build a house. Some reasons even higher and more important than the shelter reason in some ways – like providing a loving home for my family.
But for it to even be a house it needs to fulfill the basic function of protecting me from the elements.
Likewise, there are many reasons to obey the moral law, the highest being “Love of God”. But for it to even be a moral law there need to be consequences for breaking it.
Make more sense?