Paul says to the Galatians:
My friends, if anyone is detected in a transgression, you who have received the Spirit should restore such a one in a spirit of gentleness. Take care that you yourselves are not tempted (Gal 6.1).
This is an incredibly important instruction, because I've noticed in my own experience that this is a real danger. It is precisely when I've judged another person for being weak in an area in which I considered myself strong that I found I suffered from the same weakness, too, even if it did not manifest itself in the same way. This sort of thing has happened to me a number of times, and it reminds me that I am not any different or better than the other person. It is certainly true that vices are manifested differently in different persons: anger becomes murder for some while it remains "merely" hateful and spiteful in others; lust becomes philandering and adultery for some while it remains "merely" pornographic addiction for others; covetousness becomes theft for some while it remains "merely" bitter envy for others. In all cases, however, the seed of sin is present.
It is important to realize that we are not made of any different stuff than the persons in our churches who fall. Paul says elsewhere that all, both Jews and Greeks, are under the power of sin (Rom 3.9). Christ had die for me as much as for you; Christ had to die for the weak as much as for the strong. Consequently Paul tells us: Take care that you yourselves are not tempted. Precisely in those moments when you try to separate yourself from the fallen brother and think to yourself, I am not that bad; I would not have fallen in this way -- those are the moments when temptation flares up. Satan uses your judgmental attitude and arrogance to mock you and embarrass you.
Our common weakness, then, is a reason to be careful and not to judge others. Just as it is a motivation not to judge so that we are not tempted, however, it is also a reason to restore the sinner in a spirit of gentleness. Paul says that persons who have received the Spirit are to restore the fallen brother or sister in gentleness. He specifies that it is those who've received the Spirit, since the Spirit will make known to them that they, too, are weak and susceptible to fall. Those without the Spirit may not have any conception that the life they live is wrong, that they are tempted to do evil, and that they are in need of a savior. But those who have the Spirit can believe the gospel, which among other things also says that we are sinful and in need of God's grace, all of us.
This same Spirit that shows us our sin inspires us to be merciful and have pity for those who fall. Jesus emphasizes over and over again that the ethics of the Bible implies a kind of identification with the other person; it involves seeing myself in the other, including her into my circle of friends and dear ones, so that I learn to care for the other. The Spirit that convicts us of our sins helps us to see ourselves, lost and fallen, in those who've stumbled and fallen into sin. This inspires pity and mercy, just as we'd want for ourselves.