Aquinas, in Summa Theologiae (II.2.27.7), considers the question about whether it's more meritorious to love an enemy than a friend. Because on first glance, isn't it nobler to love enemies than friends? Loving friends is easy - loving enemies is hard, and has no intrinsic reward, and requires greater effort.
Aquinas has an answer: no, it's better to love your friends (but you should also love your enemies).
Firstly, we love our friends and neighbours properly, when we love them in God and from God. And, as a friend is better and closer to us, they are a more fitting object of love. So to fail to do so, to hate a friend is in fact worse than hating an enemy.
Nevertheless, Aquinas recognises that there is a different way in which love for enemies is more meritorious, because we can love friends for some other reason, but we only love enemies because of God.
I was thinking back on this passage (which I read with some students last year) as I was reading more recently in From Isolation to Community about prayer, where Werntz is considering whether it’s proper to begin our prayer with those closest to us, or does this simply reproduce "the desire to create a community in my own image":
When we begin in this way, praying for others, spurred on by our affections for them, we must recall that, in Christ, they do not exist for my love or because of their virtue toward me but because they are those who are loved by Christ. This is radical in two ways. First, those whom we would most naturally pray for, those who are most naturally valuable to us, are those whom we see now first as forgiven sinners. p140
We properly begin to re-orient our desires, in prayer, for those closest to us when we receive and welcome and love them not so much because of their closeness to us, our affinity for them, or their benevolence towards us, but in Christ. Seeing them through the mediated relationship I have with them in God, helps me see family and friends as God sees them, and so to receive them as gifts of a gracious God in my life, forgiven sinners like me.
But second, those we naturally pray for, because of their intimacy to us, become those whom we can likewise forgive, not allowing friendship and affection to obscure the need for forgiveness to mediate the best of bonds. It is not the slights of a stranger that cut us the deepest, but those of a friend. In setting aside a person’s goodness and praying for them as one for whom Christ has died, not only are the best parts of them transfigured but the wounds that they bring are also reframed. p140
Those furthest from me, the enemies with whom I may never have had a relationship, the far off people in lands I've never visited, the people whose passing acquaintance triggered dislike on their side or mine - never test me, their opprobrium slides off the skin without a mark, their rejection means little because I have never found their favour, and their wounds, even if they were the devastating physical ones of real warfare, do not penetrate to the inmost parts of who I am in God.
In praying for those closest to us, in the daily and weekly communit(ies) of life, we face the bonds that are most meaningful, and experience both the goods that are deepest, and the wounds that are the most painful. I often try to get people to realise that when Jesus is 'doing ethics', teaching us how to live, that they have to imagine they live in a small, rural village, where everybody knows each other and interacts all the time. Not because Jesus' way has nothing to do with us who live in vastly different circumstances - globally interconnected and isolated city dwellers for instance - but because starting there gives us a better vision of what Jesus means by loving enemies, praying for persecutors, leaving your gift on the altar to settle things; that vision we can carry and apply to ourselves in our own day, when we've wrestled with what it means then. The person who learns to love their enemy in their family, their workplace, their apartment complex.