Empathy, oneness, and love
I've changed. I've been different people in my own lifetime. So it's easier to see how other people are different from the person I am now, just like the person I am now is different from the person I used to be.
We change parts of our personalities like clothes. Even if you don't wear similar clothes to someone else at a point in time, you have changed clothes before and so you know that the clothes are impermanent. From this perspective, it's easier to empathize, easier to understand that there is a person wearing the clothes, that we are not our clothes. There is a human underneath the clothes. There is a soul underneath the ego.
When you realize that you are a soul underneath your ego, it's easier to look at someone else and see that they are a soul underneath their ego. It gets easier to empathize. So now you and the other person are each souls and you realize this and empathy gets easier.
The empathy gets even deeper when you start to feel that each of your individual souls is part of a larger Soul, almost even goes beyond empathy, becomes Oneness. Some say love is that sense of oneness with someone else.