 In ancient Rome there was only one sex. That sex was either fully formed into a penis or underdeveloped, no penis. Women were understood as physically inferior, less than in a fundamental way and therefore in every way. So when Paul writes of himself as the one who supplies milk, his audience would have been shocked, disgusted, scandalized. He is essentially giving up his maleness. He is speaking of himself as deformed, an inferior. Perhaps that is what it means to live the Gospel, to align ourselves with the people that society hates.