"Beware of counterfeiting the love of God by working along the line of natural human sympathy, because that will end in blaspheming the love of God."
Jesus, after his resurrection, asked his disciple Peter the same question three times (John 21:15-17): "Do you love me?" Each time Peter said, "Yes, Lord, you know I love you." Jesus' three-time reply, "Then feed my sheep." Like Peter's triptych of questioning, we are to be sure we love Jesus, then show it by spending that love on everyone else--especially "the least" of people. But if we spend love from our own human sympathy, claiming to be in the name of Jesus, we will soon be worn out, and God's love will be perceived as wearing out. But when our heart is fixed on Jesus, our spending is never exhausted because our love for Him is reflected back to us in perfect Love. That perfect love is what can't help but spill over onto even the most "unlovable."
Who do I have trouble loving? Fundamentalist Christians. Confrontational Christians. Bad drivers. Christians who make politics their religion. Rich people who think they're still "owed" something. It's easy for me to dismiss and avoid, or even slander, these people. But God wants me to love them as even He has compassion on them.
Also, when I start volunteering at the pregnancy resource center, I'm going to be tempted to love people out of my own sympathies. That's bound to wear out or come and go. But if I enter that building with love for my Savior filling my heart, I will be fixed on and filled by Him to help feed His sheep.