One of the most misunderstood doctrines among practicing Christians is that of judging others. Most would simply assert that it is never right. Don't do it! Period. But that would be to deny Scriptural teaching categorically. Truly, Matthew 7:1 teaches that we must be careful about judging other's motives. But there are other kinds of judging which God calls on his church to perform. Please listen to the following video segment from an interview with John Piper for a brief but lucid answer to this oft-confused and much avoided subject.
If you prefer the written account, click HERE.