It's because it's not from the bible. Seneca was a stoic born in Spain in 4 BC, he was active in Rome as a tutor and later advisor to emperor Nero. This passage is from his "On Providence" in which he, simply put, explains why bad things happens to good people. Christianity did however borrow some things from earlier stoical works, some of the ideas about duty and obligation to God for example. Gluttony being a sin in Christianity can be seen as a bit of fat hatred, but I haven't run across any Christian sources that puts in in any derogatory terms, or points out actual fats, but my studies of Christian texts has been very limited. Would be fun to gather more accounts of how fats has been perceived through history, there should be plenty of stuff from the later parts of the Roman empire since the rich got into some serious indulgence by then. I'll be reading a lot of Roman philosophy now so if I run across anything fun I'll share it.