It may be important to not take such words too fundamentally, materially, or carnally; as we may then judge a whole group of people as evil. If the Jesus of the Bible actually existed, and he had realized truth, then his words very likely would have been referring to peoples beliefs and not their actual physical existence being that of the devil. The devil being not a real entity, but rather those beliefs which separate us (in our minds) from the Divine.
Basically the problem with religious beliefs is the thoughtless wholesale reduction of God (our Source and Sustenance), down to a deity, a thing, an object, a particular personage. The act of such minimizing shrinks our Source (not really, but rather in the mind only) down to a fragment or piece within the universe; when actually what the word G-O-D points to, is what all universes and phenomena exist within. There is no place or time where IT is not. Does this make sense? Do you see the difference?
So, Jesus would have been speaking allegorically, in parables only. We are of the devil (of the lie) when we unquestionably believe that God is some thing outside and apart from us. It takes a huge mental process of subtraction to shrink God/Infinity, down to a specific location, as it removes God from all the rest of the universe except for some abstract little place. This is not honoring God. This is diminishing and belittling God. Yet most every Christian, Jew and Muslim does it every breathing moment of their day. These people are not evil, they are in fact no less divine than any and all life. They're just ignorant of truth and have fed upon lies. They suck the tit of Satan...allegorically speaking.
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