Mudita is sympathetic joy....feeling happiness when you experience happiness in another person.
The opposite response is envy. There is always someone, somewhere in the world who is happy. If we can tap into this we have an unlimited supply of joy available to us.
I have two friends who are sensitives.....they can perceive and interact with beings in the ghost and heavenly realms. I have no abilities in this department at all. In fact, it was hard for me to believe stories about this other world contact....until I experienced the death of my husband.
One of my sensitive friends offered to connect with my husband with me present. I wasn't going to pass up such an opportunity! The ensuing session was a little disappointing. She appeared to be having a lovely interaction, which she reported to me. But I didn't get to have any contact....which I dearly wanted.
However, I was quite impressed by the information she was passing on to me. This friend had never met my husband. So when she gave details of our relationship that were only known to the two of us, I developed confidence in consciousness surviving the death of the body, i.e. rebirth.
This confidence was reinforced when my second, sensitive friend made some comments to me, echoing exact phrases my first friend had uttered. These two people are friends of mine but have never met each other. They live in different towns.
Then, the icing on the cake happened when I visited the monastery for a retreat a few months later. When I arrived, the monk was in the middle of a tea time talk. He was talking about the heavenly realms. To my astonishment he described the fifth sensory heavenly realm in the exact same words that my friend used to describe where my husband was!
In the fifth sensory heavenly realm, whatever one brings to mind, one manifests. So, whenever I thought of this phrase, I imagined my husband doing the activities he loved to do....in perfect weather conditions! This brought me such happiness. I couldn't be sad. This is mudita....happiness for the happiness of others. Mudita was tremendously helpful in the loss of my loved one.