Perhaps that’s where we get into the weeds: where morality is closely tied to culture and vice versa. Perhaps (this is a big perhaps with a capital “P”) what separated Greco-Roman religion from the monotheistic religions was the relatively universal nature of the latter. It’s cross-cultural applicability. As someone else has commented, one idea could be that of universal human dignity (the “made in the image of God” thing). Again, I think morality as a human idea is culturally embedded and can’t be untied from culture. The Greco-Romans were moral as much as they were social. You can’t be social without having rules (hence morality). Christianity’s contribution to morality (and PERHAPS social and cultural interaction) was its universality (incorporating non-Jews and Jews within a single spiritual and embodied community).