The main argument for those of the Abrahamic religion is that God is Omnipotent and Omniscience so he decides Morality. which you would think would mean its Objective based on that argument but even then that's, not a good point.
I think it's a primitive way to think about. Abrahamic religion at its inception attempts to communicate the concepts that we have better language for today.
The morality, and especially Christian morality, isn't what you paint it to be here. It's never been static, since it's always fluid. It has its point of reference in its origins that were locked when it comes to "adoptive iterative process" once these were put on paper and maintained as such... but the process never actually stopped there. In Catholic and Jewish tradition you have a parallel Rabinic and Papal process of maintaining certain progression of moral evolution. In protestant Christianity that process is open to everyone.
The "objective" part simply means that the context is broader than any given person or even a group of people. It's a concept that flows naturally out of certain order, and we tend to accept these principles axiomatically.
For example, let's take something as simple as "don't steal". Why is it there? It's not that one day some guy woke up and said... "hear ye hear ye. I've had a dream from God... Don't Steal.", and everyone around thought "wow, how come we've never thought of that before. Brilliant!"
These principles are derived from certain higher order of being when you look at the path of changes that humanity went through in the past several thousand years. Thus, these principles are not arbitrary. They naturally flow out of the "system" that we occupy, which guides our behavior towards certain end. In Christianity such concept is equivalent to "spirit of God moving through you", but what that translates to is certain systematic patterns that we adopt, and these systematic patterns immerse from the "higher order" of complex reality and not from the simplicity we've had in the past.
Hence the term 'objective' doesn't mean "because the God said so'. It would probably better described as 'because it's inherent as a pattern of certain higher-order system'. As humans we recognize and codify these patterns, so it's no surprise that these patterns are recognized and developed in parallel in spite of the historical geographic separation we've had.
For example, the story of Moses is that of an "ascent to the mountain" to bring back certain moral code for people who are in a moral disarray once they are forced by their circumstances to wonder around in a larger group. You can read it literally, and many people do, but the meaning here is that of a necessity of a "higher order" morality once human circumstances drive us share enclosed geographic spaces. And the parallel to the golden calf here is that we generally gravitate towards our personal preferences driven by food/sex/dominance as opposed to looking at the higher-order principles that mitigate our collective being.
Hence, that form of morality is labeled as 'objective', because we don't arbitrary decide these as our preferences. We recognize these as being necessary as a part of certain functional system that we form.