Presumably the only statement of God's morality that
we have is in the Bible.
If this is the case, then we seem to have biblical
contradiction of objective morality, since God
in the OT orders his people to perform acts in his name
which are considered immoral by God in the NT.
That is, God changes his/her/its mind.
If the view of what is and is not moral can change (from God's
PoV) then how can there be objective morality?