In order to stay in a committed relationship without a deity in the life of the two who make up a couple there has to be a strong common link for each of them to the meaning of goodness. The definition of the link mirrors most religious definitions. Love, loyalty, monogamy, longevity are just a few. I’m of the opinion that the vast majority of Christian relationships are healthy and entered into by willing adults. There are always the weird ones, on both sides – the manipulative polygamist communes and the arranged marriages just outside the pedophilia envelope (these apply mostly to relationships based in religion), and the “open” relationships (which apply mostly to those relationships not based in religion) – but they are a small fraction of the verbal or written contracts healthy adults enter into the world over.
Religionists would argue that this “common link” is a God-given attribute that is instilled into each human being at birth. But that argument is only apparent in a society that accepts a “good” God as the most worshipped. A society of cannibals exhibits very few “good” attributes. Non-believers would retort that “goodness” is intertwined into the human DNA. But that argument is also only apparent in the society that governs itself with moral law. Again, a society of cannibals exhibits very few “good” attributes.
The moral law that governs a “good” society was likely instituted by men and women of religion. Or who at least recognized God as a being whom goodness can be attributed to. And the law that governs the cannibal’s society was also likely instituted by men and women of a certain kind of religion. Which kind of throws a big question in the argument that the “common link” is God given.
What is considered “good” in humanity is fostered by societal influences. From this inception it is up to each of us to carry the meaning forward.
I think what distinguishes a truly genuine “goodness” in any one person is the application of that goodness regardless of a future reward. Whether or not it is “God Given” or simply intertwined into our DNA, the true measure of a mature human being is the ability to perform good acts, and be good to others, to be loyal, to love, and to be monogamous for the long term regardless of what awaits tomorrow, in the decades to come, or in the afterlife.