As I was reading today I came across this in Heretics by C.K. Chesterton. Since I am reading through a download from Project Gutenberg I can't give you a page number but it is in Chapter 14.
We make our friends; we make our enemies; but God makes our next-door neighbour. Hence he comes to us clad in all the careless terrors of nature; he is as strange as the stars, as reckless and indifferent as the rain. He is Man, the most terrible of the beasts. That is why the old religions and the old scriptural language showed so sharp a wisdom when they spoke, not of one's duty towards humanity, but one's duty towards one's neighbour. The duty towards humanity may often take the form of some choice which is personal or even pleasurable.