From an interview with novelist and essayist Marilynne Robinson:
[Calvin] writes very beautifully about the notion that any encounter with another human being is an encounter with an image of God.
If it’s someone offending against you, it is someone that God is waiting to forgive for his offense. And so it’s a sort of triangulation where you’re not in the trenches at war with some other person.
You are thinking, “This person is sacred to God. What is God asking of me in my encounter with him or her?”
Calvin does insist that when you see a human being, you are seeing an image of God. He says that the beauty of the image should override everything and leave you with only the will to embrace that person and help them to the fullest extent of one’s means.
The idea of a human adversary is something that he virtually eliminates as a concept that is possible to a Christian person.
And when you consider that he himself was under threat of death or his whole city was under the threat of death for decades and decades and decades, he was not speaking loosely. He was talking about a time when the Inquisition was very active all around them.
So for him to say you cannot legitimately call another human being your adversary is a very, very major statement.
I don’t know how accurate this is as exegesis of Calvin, but imagine how our interactions (politics–church or secular; online conversation) would change if we took this seriously.