In my experience of various living arrangements, you can always tell the people who love each other from those who don't. The people who don't love each other are those for whom everything is a negotiation. They are chiefly concerned with "fairness," understood as the mutual recognition and satisfaction of obligations. The key to harmony is to work out a common understanding of what is due to whom, and to ensure that, on the whole, what's due is duly rendered. Everybody carries around an inner scorecard for the purpose of seeing how closely getting matches up with giving. If imbalances arise and are perceived as too great, resentment and friction ensue; if and when imbalances fail to be addressed to general approval, the living arrangement becomes intolerable. When people truly love each other, however, their chief concern is the welfare of their beloved. They do not ordinarily measure whether they're getting as much as they give; or if one of them notices an imbalance unfavorable to themselves, they do not automatically cry "unfair." They consider whether it could be rectified, and if so whether rectifying it would do the relationship, and hence the parties, true good. The greater the love, the less the willingness to count the costs and the more the willingness to pour oneself out for the beloved. In technical theological language, such love is called agape, and the self-emptying that characterizes it is called kenosis.
As the incarnate Son of God, Jesus Christ was and is the paradigm instance of such love, especially as shown on the Cross. Our love for and service to him is a participation in that love he has for us, which of course entails such love for one another. The most apparently clear instance of such love seems to be that of parents, especially mothers, for their children; but such love is to a great extent natural, explicable in terms of evolutionary biology. Where it becomes supernatural is precisely where it isn't natural. To an extent, the sacrament of marriage is an instance of that; while marriages often start out with couples being "in love" in a naturally explicable sense, and the fortunate few remain thus in love, the best marriages are those in which agape grows out of and transcends eros, so that the couple love one another all the more when they are no longer in love. But even the best marriages are often explicable in purely secular terms. The clearest instance of the kind of love we celebrate in the Eucharist is that of saints who devote their lives either to the poor and outcast or, even more strikingly, to those who don't appreciate them or even persecute them. Most of us aren't called to such a life, of course; but there's plenty of opportunity to develop and exhibit such love in all our relationships.
One way to motivate ourselves to that end is to recognize that, whatever the walk of life, true harmony and unity depend on it. Since life is never perfectly fair, relationships based on mutual utility and perceptions of fairness will sooner or later break down, or at least fail to satisfy. What we really need to be redeemed is to get beyond that, to kenotic love. And we as church are called to be the most visible instance of such love. This Triduum, let us pray and strive for that sort of unity in our relationships with each other as believers. Only that will make Christianity credible to the rest of the world.