Perhaps the best known and most often quoted verse in the Bible is Matthew 7:1, "Judge not, that you be not judged." As is often the case, this verse is frequently ripped from its context and used as a stick with which to beat others. Ironically, it becomes a means by which others are judged unjustly. It is impossible not to make judgments about people and circumstances. The whole point of Jesus' instruction is not that we should not judge, but rather that we must use a right standard when we do so. Here is the passage in context:
"Judge not, that you be not judged. 2 For with what judgment you judge, you will be judged; and with the measure you use, it will be measured back to you. 3 And why do you look at the speck in your brother's eye, but do not consider the plank in your own eye? 4 Or how can you say to your brother, 'Let me remove the speck from your eye'; and look, a plank is in your own eye? 5 Hypocrite! First remove the plank from your own eye, and then you will see clearly to remove the speck from your brother's eye. 6 Do not give what is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet, and turn and tear you in pieces." ―Matthew 7:1-6
God's Word is the only just standard by which we must all judge and be judged. If God says that something is sin, then it actually is sin and we too are (in agreement with Him) to judge it to be sin. It's sin if we do it, and it's sin if someone else does it. For example, Hebrews 13:4 says, "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge." If we are fornicators or adulterers, God will judge us, and if others are fornicators or adulterers, God will judge them. If we agree with God standard of judgment, we will make the same assessment of ourselves and of others. What we are not free to do is to make up our own standard of judgment or to have a double standard, one for other and a different one for ourselves. Hypocrisy in judgment is the misapplication of the standard of judgment. Jesus specifically call on us to make a judgment about others when He tells us to "not give what is holy to the dogs; not cast our pearls before swine."
No sinner wants to be judged. People in sin always want others to approve of their sin―it helps them feel good about themselves―it's salve to their consciences. Nevertheless, it is a deadly salve that only covers a more serious malady. The good news (the Gospel) is only good news for real sinners who turn from real sins. God's righteous standard tells us the truth about ourselves and this truth also points us to the remedy. Jesus came to save sinners from their sins. This not only means that their past sins are forgiven in Him, but also that these same sinners turn from their sins and adopt the righteous standards of judgment that God has.
"Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, 10 nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. 11 And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God." ―1 Corinthians 6:9-11