As Christians we ARE to judge all things, and are commanded to call sinners to repentance from their sin; we ARE to cry aloud and spare not; to preach out against sin; to separate ourselves from sin and from sinners and to reprove the darkness that prevails in our society -- and we ARE called upon to rebuke others at times when they are in a sin that needs to be repented of. But as we do so, we need to stay balanced -- and remember that:
1. We need to judge ourselves first.
2. We need to make sure we are judging by God's standard, not man's.
3. We need to be very cautious in judging another man's salvation who claims to be saved.
In other words, we are to judge all things -- but must judge righteous judgment.