I suppose I will be the contrarian and suggest that morality has no place in the law. Murder is not illegal because it is immoral. It is illegal because we could not have a functioning society without it. Or at least, that is the best argument for making it illegal, as the law has to do with society. There is nothing inherently immoral about driving on the left side of the road or the right side of the road. It’s just an organizational problem. We need to make sure that everyone driving in a particular area knows which side to drive on while they are in that area.
And note that this is important if we believe that religion should be separate from the law. Because while it is true that religion and morality are not the same thing, some people’s morality is wrapped up in their religion, and some people’s morality is wrapped up in their lack of religion. Furthermore, morality is often wrapped up in comprehensive philosophical convictions that are not shared by all in a way precisely analogous to religion. Deontologists do not want to be ruled by consequentialists, and consequentialists do not want to be ruled by deontologists. And those who hold a view somewhere in between do not want to be ruled by someone who holds a view somewhere else in between.
Thus we should strive to base our political decisions on reasons that are publicly available and generate an overlapping consensus. Far more relevant than ”my religion says x” would be the claim ”your religion says x (and I happen to agree, though perhaps for other reasons).” And since not everyone is religious, better still is the claim “regardless of our personal views of the good, we can all agree that x is appropriate.”
(I am summarizing—in a painfully inadequate way—an idea that has traditionally been known as the idea of public reason. Though it is frequently attributed to the Kantian tradition of political philosophy, the idea finds precedent in the work of Hobbes, Hume, and Rousseau (and perhaps others if we are willing to allow subtler forms). Indeed, it is to the idea’s credit that it itself can be the subject of overlapping consensus among such different thinkers.)