When you give someone your attention, you are giving that person your soul. You don't need to interrupt, because you are only trying to understand the other person. Understanding needs attention. Attention is kindness.
Often, we are poor listeners. The root of this problem lies in compassion. We don't have enough compassion to listen patiently, try and understand. We are distracted in our own thoughts. We are not willing to lend our soul to the other person for sometime and give attention. However, once we become sensitive to the other person, and give attention, then we have crossed the barrier of our "I" ness. Now, we are in tune with the other person. Attention is kindness.