And have no fellowship - See the sentiment here expressed fully explained in the notes on 2 Corinthians 6:14-18.
The unfruitful works - The deeds of darkness that produce no “benefit” to the body or the soul. The word “unfruitful” is used here in contrast with the “fruit of the Spirit,” Ephesians 5:9.
But rather reprove them - By your life, your conversation, and all your influence. This is the business of Christians. Their lives should be a standing rebuke of a sinful world, and they should be ever ready to express their disapprobation of its wickedness in every form.