Ephesians 5:11 And have no fellowship with the unfruitful works of darkness, but rather reprove them.

Clarke Commentary:

Rather reprove them – Bear a testimony against them; convince them that they are wrong; confute them in their vain reasons; reprove them for their vices, which are flagrant, while pretending to superior illumination. All these meanings has the Greek word ελεγχω, which we generally render to convince or reprove.

Matthew Henry Commentary:

Dare we make light of that which brings down the wrath of God?

Sinners, like men in the dark, are going they know not whither, and doing they know not what.

Walk as children of light, as having knowledge and holiness.

These works of darkness are unfruitful, whatever profit they may boast; for they end in the destruction of the impenitent sinner.

There are many ways of abetting, or taking part in the sins of others; …

by commendation, …

by counsel, …

by consent, or …

by concealment.

And if we share with others in their sins, we must expect to share in their plagues.

If we do not reprove the sins of others, we have fellowship with them.