Among the many qualities Christians are expected to have is that of being kind. “Put on then, as God’s chosen ones, holy and beloved, compassion, kindness, lowliness, meekness, and patience” (Col. 3:12 RSV). God is love, and Christians are expected to reveal that love to the world. Indeed, it is how they are to show the world what being a Christian is about (cf. Jn. 13:35). Christians are to love others, even their enemies. They are not meant to be bullies. And what, exactly, is love like? “Love is patient and kind; love is not jealous or boastful” (1 Cor. 13:4 RSV). We are to be friendly, indeed, courteous to others, considerate of them and their needs. Tolerance, not hostility, should be a part of the Christian spirit. Of course, we can acknowledge how difficult this can be. We find ourselves in all kinds of situations in which we are tested, and we end up failing to be as kind, as loving, as we should be. But this does not mean we should give up trying to do what we know is right. We should be striving for perfection, and that perfection includes developing our ability to love everyone. It is important that we don’t try to justify ourselves and our failure. We most certainly should not disregard the importance of being kind. Kindness is an integral of love. Certainly, kindness should be engaged properly. It should be embraced alongside every other good, for, as the book of Proverbs says, “He who pursues righteousness and kindness will find life and honor” (Prov. 21:21 RSV).
St. Leo the Great, therefore, pointed out that Christian integrity is to be found in and with holy kindness; that is, Christians should be holy, yes, and avoid sin, but they should do so in such a manner that they are friendly and helpful to others, acting out of charity and not judgment:
May the people of God be holy, may they be kind; holy, to refuse forbidden things; kind, to do what is commanded. Although it is a great thing to have a right faith and sound doctrine, and worthy of much praise to be circumcised in appetite, to have gentle meekness and pure chastity, nevertheless, all virtues are naked without charity, nor can nay excellence of life be called fruitful which love has not brought to birth. 
All those who try to find excuses to ignore the kindness they should show others, such, as for example, differences in belief (doctrinal disputes) do not understand the love they are expected to have. Someone can be extremely knowledgeable in regards doctrine, and live a life of extreme asceticism, but if they do it without love, without charity, it is all for naught. Christian doctrine is meant to exemplify the truth which has been revealed in and through the life of Jesus. What is that truth? It is that God is love. Those who would follow after Jesus, those who want to live out the revelation which he showed, must do so with love and grace. For it is in and through such love humanity will come together and be one. Similarly, it is through love, they will find themselves united with God.
The Spirit of Truth, the Spirit of Christ, is hindered, if not lacking, in those who claim to hold the truth while they use what they think they know as a bludgeon to confront, and indeed, abuse others. This is because the fruits of the Spirit are all related to love and the expectations of love:
But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires. If we live by the Spirit, let us also walk by the Spirit. Let us have no self-conceit, no provoking of one another, no envy of one another. (Gal. 5:22-26 RSV).
It is a kind of self-conceit, or worse, willful ignorance, which makes us think we can study, learn the doctrines of the faith, teach them to others, and yet ignore our greater calling, the calling of love, and with it, the kindness which is expected of us and still be seen as good Christians. The more we resist the way of love, and with it, the kindness which love expects of us, the more we will fall away from the truth of the faith. We can, even, be seen to be resisting grace, as grace is connected with God’s love. Thus, the more we resist love, the more unkind we become, the more all the bad qualities, all the deadly sins, will develop in us and cause us to act with malice. For, anger, resentment, and hatred will build up when love is rejected, and they will end up causing us, and those around us, much pain and sorrow (just as love and kindness helps heal such pain and sorrow and bring people to great joy). Indeed, the more we allow such hostility, and all that it brings with it, into our lives, the more we resist love and the kindness love expects from us, the more we will find people want nothing to do with us, so that in the end, only a few if any will be there for us when we need them:
The faults of anger visible in this lifetime are that you do not experience a peaceful and good mind; the joy and happiness that you had previously had perish, and you cannot regain them; you cannot sleep well; and you weaken the stability wherein your mind stays calm. When you have great hatred, even those for whom you formerly cared forget your kindness and kill you; even friends and relatives will get annoyed and leave you; although you gather others with your generosity, they will not stay; and so on. 
Being kind does not mean we should ignore or tolerate abuse. Rather, because kindness comes out of love, it will certainly have us work for and help those who are being abused. It will have us give to them the compassion and friendship they need. It will even have us resisting, with love, those who are abusive, insofar as they are abusive, hoping to change the situation so that those who are abused will no longer be abused and those who were abusing them will not only stop with their abuse but make reparations for it. Thus, it is true, we can and should confront sin, and the harm which it causes, but we must do so in the spirit of charity, and so, being as kind as possible. And indeed, the kinder we are, the more we will find we will be able to change things, because we will be living out the truth in charity, giving the right example, an example which will be attractive to others as they naturally feel joy and gladness when being treated with kindness. Thus, kindness will help draw people together:
Kindness, when combined with humility, obedience, and meekness, is a catcher of good things, a gatherer of all the virtues, and an abode for the Holy Trinity. Kindness, when combined with humility and obedience, binds together those who persevere ascetically and does not allow separation from one another. 
If we have any question as to what this means, we should once again look to God and God’s loving patience with us:
In spite of all these things, God remains well disposed toward everyone. To no one does he deny his mercy. Why, he even bestows many good things indiscriminately upon all. He prefers to invite with acts of kindness those whom he could rightly subdue with punishments. Delay in retribution makes room for repentance. It cannot be said, however, that there is no vengeance where conversion does not take place. For, a hard and ungrateful mind becomes already its own punishment. It suffers in its conscience whatever has been deferred by the goodness of God. 
Thus, though many rage against kindness, thinking that in doing so, they work to preserve the truth of the faith, all they do is counter the faith itself. They give a false vision of the truth, one which ultimately has them making a false, idolatrous image of God. When they do so in the name of Christ, they do so by subverting Christ and what he stood for. What they offer is a false Gospel, filled with such hostility, such anger and malice, it can only come from the spirit of an anti-Christ.
 Tsong-kha-pa, The Great Treatise on the Stages of the Path to Enlightenment. Volume Two. Trans. Lamrin Chenmo Translation Committee. Ed. Joshua W.C. Cutler and Guy Newland (Ithaca: NY: Snow Lion Publications, 2004), 157-8.
 Moralia et Ascetica Armeniaca: The Oft-Repeated Discourses. Trans. Abraham Terian (Washington, DC: CUA Press, 2021), 176 [Discourse 11].
 St Leo the Great, Sermons, 153-4 [Sermon 35].