Here’s a question. Christians are perfectly moral if they eat ham. Jesus fulfilled the law and now allows it. Jews, however are immoral if they eat ham. They feel the law is still in effect for them. Should we base any current legislation on the eating of ham? Or, should we be able to accept that ham is perfectly moral for Christians and immoral for Jews? It seems there are cases where morality isn’t just what the Christian God decides. Since this is a case where either side isn’t too bothered by what the other side believes, we usually don’t think about it.
I suspect your confusion is the result of a unspecified definition of morality.
In Scripture, for example, the Mosaic Law that bound the Israelites and later the Jews was comprised of moral, liturgical and practical laws. They weren’t all moral. The rules against eating pork had to do with ritual purity because pork was regularly an aspect of pagan sacrifice. Circumcision was another. These were meant to separate the Israelites from their pagan neighbors who worshiped and sacrificed to idols.
Such laws were part of covenants, of which the covenant at Mount Sinai was only one of seven in total. Each covenant came with slightly different terms of agreement – i.e., the people would do this and in return God would do that.
The place of the different laws was to regulate behaviour. Some laws were practical, much like traffic laws today, and could change. Others were liturgical and tracked the faithfulness of the people to God. Moral laws would be those that apply to all people at all times because they are derived from the nature of human beings vis a vis creation as a whole. The Ten Commandments would be the moral law. The Mosaic Law in Deuteronomy (the Second Law) was assembled by Moses to provide a social blueprint – providing the specifics in terms of how the moral law would be carried out day to day – for the people to obey to show their covenant agreement with God. Leviticus would be more liturgical in terms of spelling out what ritual purity involved.
This is general, though and there are intermixtures of types of laws between the books of the OT.
If God exists, then morality is precisely what God “decides” because God, properly understood, is the determiner of the nature of reality. God is
fundamental reality properly speaking, so the nature of what it means to exist in reality is what determines the nature of morality.
We may not see that or understand that, but that would be because we don’t fully apprehend the nature of reality or God. We don’t even properly understand our own nature or existence, but that might be part of the moral journey we are on as individuals and as a collective of individuals.