We know certain actions are right and wrong therefore morals are objective. If morals weren't objective and were standing in line somewhere, and I cut in front of you... You have no right telling me that my action that I took was wrong. It is really common sense talking about objective morality(to me).
If there were a perfect god by subjective standards then that god wouldnt be perfect at all. Anyone can be perfect according to a morality that they made up. If god had an objective morality then he didnt created it he merely learned it. And christian morality and any other religious morality is subjective i know this because they all contradict each other and cannot all be objectively right. A true religion that was actually from and ALL KNOWING GOD god would make man made religions look like the work of children. And sense none are more profound to be from men i have no reason to suppose their is a true religion from a god smart enough to come up with the laws of physics. But religion doesnt teach objective moraity because it wasnt inspired by it. It was inspired by our leaders desire to make life better for themselves. So their desires have to be legal which they wouldnt be if we didnt agree with them. Also we couldnt have war if everyone knew objective morality by your views because you believe most people try to be good. Its a fact that the conscience consists of vague reminiscences of precepts heard in early youth and most people use those feelings they call a conscience instead of thinking analytically for determining the moral status of any act. .
If a perfect god, who knew everything created a moral code to live your life by that book of law would be absolutly good no matter how old it got. No one would need to question it because our own ethics of right and wrong would not conflict with it.
There also is not really "knowing about right and wrong." Even if we are hypothesizing about gods or "higher beings" than us earthly humans, it is the case that those beings too, may have their opinion; it is not that it would be anything external to them. Still subjective (to them), and not objective.
Even if the god was perfect, it would still rely on humans in the religion. No matter what the god states, a human would eventually warp the meaning. This is because humans are not perfect and are prone to misinterpretations. I would guess it is because they add their own emotions to what was meant.