Nearly all of Christian discourse seems to be focused on morality - indeed, before I was a Christian that was all I could perceive of it. Yet - as I then realized - to discuss morality in isolation is all-but meaningless; and especially when the prevalent 'cosmology' is entirely materialist and scientistic.
In other words; Christian morality makes no rational sense if the universe operates and life evolved on the basis described in mainstream science - and assumed to be The Whole Truth (in some kind of crude form) by the entirety of influential public discourse in all developed nations.
What is needed is to relate Christian morality to our understanding of the nature of reality.
(A better - because more general - word for what I mean is metaphysics; but I am focusing here on the cosmological aspect - on how the universe happened, and - in particular - how life and mankind happened.)
An anecdote may help clarify: Whenever (as an atheist) I thought about some aspect of Christian morality - such the Ten Commandments, the Sermon on the Mount, or any distinctive Christian church teaching in conflict with the mainstream - I would be faced by the incompatability of this with the way the universe worked.
By what possible mechanism - I thought - could we get specific moral teachings, relating - for example - to sex and sexuality - from a universe that had formed on the basis of physics, and a life that had evolved by natural selection?
Where could any real, objective, true morality possibly have come-from - given these materialistic ingredients for he world and everything on it?
In sum - you can't get morality from the ultimate explanations of physical reality - such as quantum theory, relativity or whatever; neither can you get morality from natural selection properly understood (at most, natural selection can yield a delusion of morality).
By failing to tackle and express Christian cosmology; Christianity relegates its morality to the level of an arbitrary construct - merely a matter of opinion or expediency.
If not - then what? What ought Christians to do instead?
In the first place - Christians need to start at the beginning, and emphasize that this is a created universe; and that God is The Creator.
Only in such a context can we discuss any real, objective, universal morality.
And lacking such a context All morality will be arbitrary and expedient - as indeed mainstream, modern, secular-left morality explicitly acknowledges itself to be - when compelled to answer the question*.
But secular morality has the vast proximate 'advantage' over Christian morality of being backed by most of the world's power, propaganda and money...
The only expedient reason, therefore, for accepting Christian rather than secular-left morality is that Christianity is true, and that truth matters.
And that is a matter of ultimates: including of cosmology.
*Note: If the universe (and life) originated and is sustained by 'science explanations'; then reality has neither purpose nor meaning. Without purpose and meaning, there can be no real morality; but only arbitrary human constructs. There can then be no coherent discussion of morality at all. Attempts to construct a morality based on pleasure-pain probabilities (e.g. utilitarianism) are equally arbitrary; since there are no grounds for saying either than pleasure is better than pain, or that the happiness of the community is more important than that of an individual - and no grounds for arguing against short-termist selfishness and unconstrained manipulation and exploitation. All possible values hinge on this question of whether reality is created, or 'just happened'.