I have seen many Christian leaders denouncing the sin of racism (especially of late), but I have not seen any clarification of what this sin consists in, given that "racism" has been defined in myriad ways. If it means "hatred of another person because of their race", then it is clearly a sin, because hatred is, in itself, sinful.
So I shall use "racism" to mean "the belief that there are significant (according to worldly ways of judging) and non-superficial differences between various races." This excludes differences in melanin content, which are superficial, and differences in kidney function, which everyone regards as insignificant. However, it includes differences in long-distance running ability, which, however insignificant from a Christian standpoint, are considered significant by the secular world when the Olympics roll around. Is this form of racism sinful? More broadly, how should the sin of racism be understood?