"Even if we perform upon thousands of good works, my brethren: fasts, prayers, almsgiving; even if we shed our blood for our Christ and we don’t have these two loves [love of God and love of brethren], but on the contrary have hatred and malice toward our brethren, all the good we have done is of the devil and we go to hell. But, you say, we go to hell despite all the good we do because of that little hatred?
Yes, my brethren, because that hatred is the devil’s poison, and just as when we put a little yeast in a hundred pounds of flour it has such power that it causes all the dough to rise, so it is with hatred. It transforms all the good we have done into the devil’s poison."
-St. Kosmas Aitolos