Some people are the world to us, and others hardly matter at all. Strangers do not compel us to compassion, but rather to caution, fear, and exclusion. But Christ teaches us that our moral obligations extend beyond those whom we know and trust. He teaches us that the mere presence of a stranger, makes him a neighbor, and thus worthy of love. (Bloom, 2013)
The system of mirror neurons stands at the forefront of empathy. It makes us feel what others feel. It is a basic level of connection, of humanity. Take a simple emotion: disgust. When shown videos of people smelling a foul odor, participants watching the facial expression on a screen showed activation in the anterior insula. Observing an emotion in others activates the neuronal representation of that emotion in us (Wicker, 2003). Our own brains connect the gap between us and a stranger.
Book Recommendation: Against Empathy by Paul Bloom
Reference: (Bloom, 2013) (Wicker, 2003)