Here's the quote:
You see, love is not an abstraction. It’s not a theory or a cosmic force or a slogan or any kind of diffuseness spread across the world. Love is particular. You do not love in general, you love this person, this thing, this life, you love this, this, this, this, this, and this, and this, and this loves you back. This is the only thing in the world, and it is precise and specific and real, and it is everything and infinitude.
What I'd add to this quote, from a Christian perspective, is the theme of Stranger God: Love is hard. Loving the specific and particular brings us into intimate, difficult contact with the demands of love. Consequently, we try to avoid these demands by escaping into the abstract, universal and general. We recoil from the demands of love and back up.
In this chapter, a lady of "little faith" is in conversation with the spiritual elder Zosima. The lady of "little faith" is a wealthy Russian woman who petitions the elder to bless and heal her daughter. In making that petition the lady describes her spiritual predicament, her struggles to love people. More specifically, the lady loves people in the abstract. Her struggle boils down to loving the specific, particular people in her life. Hearing these struggles, the elder responds by telling of a man he once knew:
He was an old man, and unquestioningly intelligent. He spoke just as frankly as you, humorously, but with a sorrowful humor. "I love mankind," he said, "but am amazed at myself: the more I love mankind in general, the less I love people in particular, that is, individually, as separate persons. In my dreams," he said, "I often went so far as to think passionately of serving mankind, and, it may be, would really have gone to the cross for people if it were somehow suddenly necessary, and yet I am incapable of living in the same room with anyone even for two days, this I know from experience. As soon as someone is there, close to me, his personality oppresses my self-esteem and restricts my freedom. In twenty-four hours I can begin to hate even the best of men: one because he takes too long eating his dinner, another because he has a cold and keeps blowing his nose. I become the enemy of people the moment they touch me," he said. "On the other hand, it has always happened that the more I hate people individually, the more ardent becomes my love for humanity as a whole."
"The more I love mankind in general, the less I love people in particular." As the elder Zosima will go on to observe, real love is "a harsh and dreadful thing." And what makes it difficult are the concrete and particular demands of concrete and particular people.
This is why, as I describe in Stranger God, the Little Way of Thérèse of Lisieux is so potent and powerful as a spiritual discipline. As I describe it, the Little Way is a practice of loving the specific and particular, especially when the specific and particular is hard, difficult and demanding. This is hugely important, as the demands of love require a good degree of virtue. Warm aspirations are not enough to get us through the trials of love. Love demands grit, and the practices of the Little Way help form this toughness.