If morality as presented as God's will, then this tends to strike a modern atheist as His opinion against mine. Why should God's morality be right and mine wrong; why should God get to set the rules for everybody?
The reason is that true morality is not detachable from reality, but interwoven inextricably - God is creator, and what we call morality is just one aspect of reality that we have picked-out and called morality.
So God's rules apply to us because God created us and everything in our world... but the moderately-sophisticated atheist will soon pick up the inconsistency in this argument... If God created everything including myself, how and why is there a conflict between what I want to do and what God wants me to do?
The answer is 'free will' - but where does freedom come-from if God has created everything? It doesn't make sense.
And - more profoundly - why did God make Men with free will? What is the intention of this - if not to sin, then how are Men supposed to use their free will? If the answer is merely to choose to obey God, then this choice is pointless - God might as well have made Men to obey in the first place!
My different understanding is that God created our reality, our 'universe'; but God did not create our free will: free will comes from our-selves.
And further that God is not primarily aiming at obedience; but instead at Men becoming gods.
My understanding is that God could not make men as already-gods - because being a god entails free will; so the intention is that individual Men will choose to grow and develop towards divinity.
So... God has created the reality in-which we dwell; and morality is part-of living in alliance with the nature and purpose of God's creation; living aligned-with reality. But free will comes from that part of our reality which God did not create; hence the conflict intrinsic to this life.
If we choose Not to live in alignment with creation-reality (to reject God's virtue, truth, beauty in unity), this is a rational choice; but ultimately that negative choice-to-reject condemns the rejector to life outside creation.
What is outside creation? In essence nothing; that is chaos, lack of meaning, no purpose, zero relationships.
But modern Man does not believe-in the reality of meaning, purpose, or permanent personal relationships... indeed modern Man regards all of these as tyranny, and would actively reject them.
So be it: if modern Man does not want them, then he is free to reject them.
What would he get instead? He would get his own way - complete freedom in a context of total isolation. If modern Man really does not want to be a part of creation, if modern man wants his own personal autonomy above everything; he will presumably choose to reject creation - including God's morality.
From this you can see why love is the key for Christians; love is the positive reason why you or I or anybody else would actively-want to embrace the reality of God's creation; and eschew the absolute isolation that total autonomy would entail.