Julian of Norwich has an excellent little passage in Revelations ch. 76:
The soul that willeth to be in rest when [an] other man’s sin cometh to mind, he shall flee it as the pain of hell, seeking unto God for remedy, for help against it. For the beholding of other man’s sins, it maketh as it were a thick mist afore the eyes of the soul, and we cannot, for the time, see the fairness of God, but if we may behold them with contrition with him, with compassion on him, and with holy desire to God for him. For without this it harmeth and tempesteth and hindereth the soul that beholdeth them. For this I understood in the Shewing of Compassion.
In other words, for your own good you should regard no one's sin, even in thought, unless you regard it with sympathetic contrition, with compassion, and with "holy desire to God". I think this is right; but it is something exceedingly difficult to do.
Human beings are not good at sympathetic contrition, even setting aside times when we are too inclined to condemn. We have this sneaking tendency to try to substitute something else for contrition with our fellows -- forgiveness, oftentimes -- even when such a substitution would be a blasphemous presumption. Contrition with another is rare; it is something we usually only exhibit in the case of family and friends (and it is rare even then). Contrition is a melting of the hardened heart, a sorrow of the will, a tearing of oneself away from the merely apparent good so that one may pursue the true good. We normally think of it as something we do for ourselves; but, as Julian notes, we can also have contrition with another. How can one be contrite with another when one is not culpable? But, rare as it is, it does occur, as I said, when we are contrite with a family member or a friend simply because they are one of our own. And it is only rational that it should be so. When all the accounts are settled, and you are shown to be wholly innocent of an evil deed -- is it really a complete consolation that you were not the one who did the evil deed? When children are torn from their homes and blood flows like rivers, when the poor are trampled and the weak are destroyed, can you, as a reasonable person, rest in full comfort knowing that you are not the one causing these things? Does your innocence give you total relief, knowing that the ones who do these things are like you, that you are human and so are they, and that they are therefore, however distantly, one of your own? When we rest in our blamelessness is there not some part of us that we must actively distract from the sad and sorrowful truth: that the monsters who roam the earth are human, even as we are, and that because of that, their sin is the sin of one of us. When vindication comes and you find you do not need to say, "Lord, forgive me," is there not still some real meaning, however weak and faint, to saying, "Lord, forgive us," not because you are guilty but because, whatever horrible thing has happened, there is still this ineliminable us? Take the worst and most wicked, and look at their faces, and see it for yourself: they may be the guilty, but they are one of our own, and in them we are faced with this terrible thing: that, innocent as we may be, this deed was not irrelevant to us; we did not do it, but we are not free from it; it was done by one of our own. They too are human, even as we are. There is, in this sense, a deep and crushing sorrow to being human: that one of us can do such things is a terrible thing. This is only half the story, for there is an equisite joy to being human. We distract ourselves from that, too. But we go out of our way to distract ourselves from the melancholy of humanity, the sadness and grief of knowing that a human being, like ourselves in so many ways, can stoop so low. And that sorrow, even if merely recognized rather than felt, is the start of contrition, the beginning of tearing ourselves (not just myself, not just yourself, but ourselves) away from the apparent good that trapped us (not just me, not you, but one of us), the beginning of turning toward the good we (not just me, not just you, but we) truly need.
As with evil, so with serious error. Do not regard the serious error of another unless you can regard it having contrition with the one in error; the one in error is one of your own.
And such contrition is the ambience of true compassion; not the false compassion we have for someone we think of as being in no way connected with us, but the true compassion we have for one of our own who has in some way failed. For failure is what it is: they have failed to be as excellent in their humanity as they might have been; and that, too, is a sad and terrible thing, a cause for mercy. That someone, for instance, should deliberately mislead others on important matters is not merely terrible because people have been misled; it is terrible because one of us has fallen into such a state that they could do such a thing. That they are guilty cannot be ignored; and the 'they' is not someone indifferent to us, but one of us. They too are human; they are one of our own. We like to define things in terms of Us and Them. That is fine. Indeed, it is often the case. But it must never be forgotten that 'Them' is always just a more distant 'Us'. 'They', when they fail, are not so very different from one of us, when one of us fails; and the need for compassion, mercy, pity, whatever you wish to call it, is a flower that grows in the distant fields of 'Them' just as much as it grows in the nearer fields of 'Us'. And, again, as with evil, so with error; if it is possible in the stronger case, it is possible in the weaker case. If we were in error, and they were in the right; would it not be a worthwhile thing that they had compassion for us rather than contempt? How can we take their error as an occasion for dismissal when we would rebel against such a thing were our places reversed?
And it can never be wrong to wish one of us well. God knows we all need such well-wishing. There is an image in Dickens somewhere (A Christmas Carol, I think): the absurdity of the insect on the leaf begrudging his fellow insects in the dust their lives. It is meant, I think, to say something about social classes; but the principle encapsulated is general. If we find ourselves, by chance or by diligence, to be insects on the leaf, can we honestly, and reasonably, begrudge our fellow insects in the dust a bit of civility, a bit of well-wishing, a bit of merciful teaching, one more chance at coming to understand? However right we may be, however perverse they may have been, can we seriously consider it just too much to allow that they too can learn? Can the insect on the leaf without absurdity begrudge the insect in the dust one more chance at enlightenment?
Thus can teaching be an act of mercy: when we do not regard the follies of another unless we can do so having contrition with him (for when one of us goes astray, that is an occasion for both of us renewing our resolve to find truth, for they are not simply some distant thing of no concern, but one of our own), and having compassion on him (for it is a grievous thing to be in error, and we, too, might be in error one day; we and they are much alike), and having a holy desire to God for them (for it is always rational to hope that those of us who have failed may begin to do better). In all this, of course, I am talking about teaching those who do not know something truly important what they need to know; that is, the teaching of things needful. If it was needful for us, can we seriously begrudge it to others who find it needful?
Teaching begins not in the finding of people who already know; it begins in the hope that people who do not already know may yet come to know. Even when we are only talking about the most important things to be taught, it is possible to teach just by happenstance, or because that's just what you do to get by. But it is also possible to teach because the people you are teaching are your own, however tenuously the label 'your own' may be applicable to them. It is possible to teach because the people you are teaching are human, and you do not consider it acceptable that another human should not also have the chance to learn it (for you yourself are as human, perhaps even as absurdly human, as they are; no matter how conveniently you might sometimes forget it, you and they are thrown in together as both of one kind). Can we stand by idly when our own wander lost? Such mercy, like every other sort of mercy, is not the sort of thing that can be demanded; but it is the sort of thing to which we can find ourselves called.