Jesus in Matthew 7:1 is pointing out a warning to those who judge others: “Remember, you are going to be judged yourself.” He take the caution a step further by saying that you will be judged in the same way you judge others. Notice that He goes on to give an illustration of hypocrisy. Generally those who are making a big deal over the sins of others actually have even greater problems themselves–whether or not those problems can be seen by others.
Perhaps an insight to this comes to us from Jesus’ parable in Matthew 18:21-35. Here we see that the king who forgives the debt of a servant expects the servant to do so to those in debt to him. When the king finds out the servant treated the servant’s debtor without the same compassion, the king calls the servant in and treats him the same way–by turning him over to the inquisitors and demanding repayment. Thus if we judge without mercy, then God will judge us without mercy. If we make hasty judgments on the outward man and neglect to see the inner man, will not God do so to us? This is a powerful and fearful idea.