A variety of simple, trivial acts of kindness often have their moral value drastically overestimated. As a result of this faulty emphasis, it is easy for a superficially kind person to develop a reputation for being genuinely good even if he or she believes in morally horrific ideas, since all it takes to convince many people is subtly shifting the emphasis to petty but visible acts of kindness. The ease of this deception can obscure the fact that many particular acts of kindness are not objectively important. If the value of kindness is so distorted, what place within a sound ethical framework is there for it? Yes, some Biblical verses (such as 1 Corinthians 13:4 and Ephesians 4:32) classify kindness as morally good, but this does not mean that one has an obligation to be kind to everyone at all times.
Before I proceed, I want to clarify that I am very grateful for opportunities to display kindness towards people whom I respect or love in the sense of appreciating them as individuals, not merely in the impersonal sense God prescribes for each person to show towards all others (the Bible never commands one to have strong personal affection for every living human). However, kindness is not the objective of every interaction I have with another person. Is kindness good? As long as it does not interfere with justice, yes. Nevertheless, it is often not obligatory.
Does someone sin if they do not hold the door open for another person? Do they sin if they do not speak to strangers in a distinctly pleasant tone? What makes one random act of kindness obligatory as opposed to another? Since a person could always be more kind, such as by making an additional kind statement or performing an additional benevolent deed, practically any line drawn is purely arbitrary. It is futile to argue that someone should go beyond what is obligatory, since such an argument entails the idea that someone has an obligation to do that which they have no obligation to carry out.
Kindness is not itself the supreme goal of morality. Instead, it is largely supererogatory in many relationships--a marital relationship or friendship should be marked by mutual kindness to at least some degree, but this does not mean that one is obliged to perform particular acts of unecessary kindness for strangers. To reduce Christianity to a system featuring a God who saves us merely so we can be superficially kind to others is to trivialize genuine Christian morality and Yahweh's nature alike. Kindness is not at the core of Biblical moral obligations. Indeed, even the Christian conception of love can seem deeply unkind to some individuals under the right circumstances. Truth and justice, above all else, are the foundations of Christian morality.
Instead of always wondering about whatever course of action will display the most kindness, the first ethical question a Christian should ask himself or herself pertains to whether or not an action is just according to the Bible. Justice does not necessarily exclude kindness, but it can be hindered by a surplus of the latter. The core of morality is ultimately about treating God, other people, and even animals according to what they deserve, which is about not violating one's obligations towards them; anything else that is good can only be supererogatory. Treating someone in a way that does not violate any obligations towards them is a matter of justice, not one of kindness. Justice, therefore, should be the chief concern of moralists.