He that saith he is in the light, and hateth his brother, is in darkness even until now. He that loveth his brother abideth in the light, and there is none occasion of stumbling in him. But he that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes.
I John 2:9–11

The new commandment of which John speaks is the greatest commandment of all: to love.
‘What is the greatest commandment?’ the young lawyer asked the Master.
And Jesus said, ‘How do you read it?’
‘Love the Lord thy God with all thy heart and soul and mind and strength,’ the lawyer answered.
‘That’s it,’ Jesus said. ‘And the second is like unto it: Love thy neighbor as thyself’ (Matthew 22:36–39).

The fresh word for you and me is that we are to love, for if we say we’re walking with the Lord and are close to the Lord but have hatred in our hearts towards our brother, then something is not right.
It’s a wonderful thing to be able to say, ‘To the best of my knowledge, I’m not bitter towards anyone, mad at anyone, or angry with anyone because I know what a sinner I am. I know how much I’ve failed. I know how gracious God has been to me.’ When that’s our heart, we know things are right.

Courson, Jon: A Day's Journey : 365 Daily Meditations from the Word. Santa Ana, CA : Calvary Chapel Publishing, 2003, S. November 26